[grubcfg] fix inter-module dependency with plymouthcfg modules

The plymouthcfg Calamares module is optional. Distributions which
  write filesystems with a full plymouth configuration won't even
  want to use it (see plymouthcfg docs).

  However, now grubcfg depends on plymouthcfg to run because
  the globalstorage value to trigger setting  'splash' in grub,
  is set in the plymouthcfg module.

  Just check for plymouth existence separately in the grub module.

  Fixes ea1c8a0e5d

src/modules/grubcfg/main.py

@@ -44,16 +44,21 @@ def modify_grub_default(partitions, root_mount_point, distributor):
     dracut_bin = libcalamares.utils.target_env_call(
         ["sh", "-c", "which dracut"]
         )
-    have_dracut = dracut_bin == 0  # Shell exit value 0 means success
+    plymouth_bin = libcalamares.utils.target_env_call(
+        ["sh", "-c", "which plymouth"]
+        )
+
+    # Shell exit value 0 means success
+    have_plymouth = plymouth_bin == 0
+    have_dracut = dracut_bin == 0
 
     use_splash = ""
     swap_uuid = ""
     swap_outer_uuid = ""
     swap_outer_mappername = None
 
-    if libcalamares.globalstorage.contains("hasPlymouth"):
-        if libcalamares.globalstorage.value("hasPlymouth"):
-            use_splash = "splash"
+    if have_plymouth:
+        use_splash = "splash"
 
     cryptdevice_params = []
 

src/modules/plymouthcfg/main.py

@@ -40,14 +40,9 @@ class PlymouthController:
                          "/etc/plymouth/plymouthd.conf"])
 
     def detect(self):
-        isPlymouth = target_env_call(["which", "plymouth"])
+        isPlymouth = target_env_call(["sh", "-c", "which plymouth"])
         debug("which plymouth exit code: {!s}".format(isPlymouth))
 
-        if isPlymouth == 0:
-            libcalamares.globalstorage.insert("hasPlymouth", True)
-        else:
-            libcalamares.globalstorage.insert("hasPlymouth", False)
-
         return isPlymouth
 
     def run(self):