[packages] Convert command-failures into readable error messages

If the pakcage manager fails in some way, convert to a readable
error message instead of leaking the exception to the caller
(which produces a traceback, which is harder to read and less
informative)

src/modules/packages/main.py

@@ -579,11 +579,27 @@ def run():
 
     update_db = libcalamares.job.configuration.get("update_db", False)
     if update_db and libcalamares.globalstorage.value("hasInternet"):
-        pkgman.update_db()
+        try:
+            pkgman.update_db()
+        except subprocess.CalledProcessError as e:
+            libcalamares.utils.warning(str(e))
+            libcalamares.utils.debug("stdout:" + str(e.stdout))
+            libcalamares.utils.debug("stderr:" + str(e.stderr))
+            return (_("Package Manager error"),
+                    _("The package manager could not prepare updates. The command <pre>{!s}</pre> returned error code {!s}.")
+                    .format(e.cmd, e.returncode))
 
     update_system = libcalamares.job.configuration.get("update_system", False)
     if update_system and libcalamares.globalstorage.value("hasInternet"):
-        pkgman.update_system()
+        try:
+            pkgman.update_system()
+        except subprocess.CalledProcessError as e:
+            libcalamares.utils.warning(str(e))
+            libcalamares.utils.debug("stdout:" + str(e.stdout))
+            libcalamares.utils.debug("stderr:" + str(e.stderr))
+            return (_("Package Manager error"),
+                    _("The package manager could not update the system. The command <pre>{!s}</pre> returned error code {!s}.")
+                    .format(e.cmd, e.returncode))
 
     operations = libcalamares.job.configuration.get("operations", [])
     if libcalamares.globalstorage.contains("packageOperations"):
@@ -603,11 +619,18 @@ def run():
     for entry in operations:
         group_packages = 0
         libcalamares.utils.debug(pretty_name())
-        run_operations(pkgman, entry)
+        try:
+            run_operations(pkgman, entry)
+        except subprocess.CalledProcessError as e:
+            libcalamares.utils.warning(str(e))
+            libcalamares.utils.debug("stdout:" + str(e.stdout))
+            libcalamares.utils.debug("stderr:" + str(e.stderr))
+            return (_("Package Manager error"),
+                    _("The package manager could make changes to the installed system. The command <pre>{!s}</pre> returned error code {!s}.")
+                    .format(e.cmd, e.returncode))
 
     mode_packages = None
 
     libcalamares.job.setprogress(1.0)
-    libcalamares.utils.debug(pretty_name())
 
     return None