[services-*] Fix translations

- Strings like "{} the {} with {}" are terrible for translators:
   - no context
   - no possibility to re-order grammatical units
   - substituting in English parts-of-speech is going to make a mess
 - Write the strings out with explicitly named substitutions,
   no part-of-speech substitution, and better formatting.

src/modules/services-openrc/main.py

@@ -56,6 +56,22 @@ class OpenrcController:
         self.initdDir = libcalamares.job.configuration['initdDir']
         self.runlevelsDir = libcalamares.job.configuration['runlevelsDir']
 
+
+    def make_failure_description(self, state, name, runlevel):
+        """
+        Returns a generic "could not <foo>" failure message, specialized
+        for the action @p state and the specific service @p name in @p runlevel.
+        """
+        if state == "add":
+            description = _("Cannot add service {name!s} to run-level {level!s}.")
+        elif state == "del":
+            description = _("Cannot remove service {name!s} from run-level {level!s}.")
+        else:
+            description = _("Unknown service-action <code>{arg!s}</code> for service {name!s} in run-level {level!s}.")
+
+        return description.format(arg=state, name=name, level=runlevel)
+
+
     def update(self, state):
         """
         Call rc-update for each service listed
@@ -83,19 +99,28 @@ class OpenrcController:
                         warning("Cannot {} service {} to {}".format(state, name, runlevel))
                         warning("rc-update returned error code {!s}".format(ec))
                         if mandatory:
-                            return (_("Cannot {} service {} to {}").format(state, name, runlevel),
-                                    _("rc-update {} call in chroot returned error code {}").format(state, ec)
+                            title = _("Cannot modify service")
+                            diagnostic = _("<code>rc-update {arg!s}</code> call in chroot returned error code {num!s}.").format(arg=state, num=ec)
+                            return (title,
+                                    self.make_failure_description(state, name, runlevel) + " " + diagnostic
                                     )
                 else:
                     warning("Target runlevel {} does not exist for {}.".format(runlevel, name))
                     if mandatory:
-                        return (_("Target runlevel {} does not exist for {}.").format(runlevel, name),
-                                _("No {} found.").format(runlevel_path))
+                        title = _("Target runlevel does not exist")
+                        diagnostic = _("The path for runlevel {level!s} is <code>{path!s}</code>, which does not exist.").format(level=runlevel, path=runlevel_path)
+
+                        return (title,
+                                self.make_failure_description(state, name, runlevel) + " " + diagnostic
+                                )
             else:
                 warning("Target service {} does not exist in {}.".format(name, self.initdDir))
                 if mandatory:
-                    return (_("Target service {} does not exist.").format(name),
-                            _("No {} found.").format(service_path))
+                    title = _("Target service does not exist")
+                    diagnostic = _("The path for service {name!s} is <code>{path!s}</code>, which does not exist.").format(name=name, path=service_path)
+                    return (title,
+                            self.make_failure_description(state, name, runlevel) + " " + diagnostic
+                            )
 
 
     def run(self):

src/modules/services-systemd/main.py

@@ -65,8 +65,24 @@ def systemctl(targets, command, suffix):
                 "systemctl {} call in chroot returned error code {}".format(command, ec)
                 )
             if mandatory:
-                return (_("Cannot {} systemd {} {}").format(command, suffix, name),
-                        _("systemctl {} call in chroot returned error code {}").format(command, ec)
+                title = _("Cannot modify service")
+                diagnostic = _("<code>systemctl {arg!s}</code> call in chroot returned error code {num!s}.").format(arg=command, num=ec)
+
+                if command == "enable" and suffix == ".service":
+                    description = _("Cannot enable systemd service <code>{name!s}</code>.")
+                elif command == "enable" and suffix == ".target":
+                    description = _("Cannot enable systemd target <code>{name!s}</code>.")
+                elif command == "disable" and suffix == ".service":
+                    description = _("Cannot enable systemd service <code>{name!s}</code>.")
+                elif command == "disable" and suffix == ".target":
+                    description = _("Cannot disable systemd target <code>{name!s}</code>.")
+                elif command == "mask":
+                    description = _("Cannot mask systemd unit <code>{name!s}</code>.")
+                else:
+                    description = _("Unknown systemd commands <code>{command!s}</code> and <code>{suffix!s}</code> for unit {name!s}.")
+
+                return (title,
+                        description.format(name=name, command=command, suffix=suffix) + " " + diagnostic
                         )
     return None