Fixed paths for lsc and locales commands

Subiquity snap doesn't stage language-selector-common nor locales
packages.
Attempting to run those commands require respecting the env previously
prepared by the caller, as well as fixing the commands paths
(or changing the PATH env var in the env preparation step).
Since the apt commands were already ran with a fixed path,
I'm applying the same principle in here.
Yet, for now, Jammy doesn't ship the l-s-c package seeded,
so a condition was preserved to avoid future crashes.

system_setup/server/controllers/configure.py

@@ -91,7 +91,9 @@ class ConfigureController(SubiquityController):
 
     def __update_locale_cmd(self, lang) -> List[str]:
         """ Add mocking cli to update-locale if in dry-run."""
-        updateLocCmd = ["update-locale", "LANG={}".format(lang),
+        # A fixed path should be ok here since all releases (so far) ship
+        # the locales package.
+        updateLocCmd = ["/usr/sbin/update-locale", "LANG={}".format(lang),
                         "--no-checks"]
         if not self.app.opts.dry_run:
             return updateLocCmd
@@ -123,13 +125,12 @@ class ConfigureController(SubiquityController):
 
         return True
 
-    async def __recommended_language_packs(self, lang) \
+    async def __recommended_language_packs(self, lang, env) \
             -> Optional[List[str]]:
         """ Return a list of package names recommended by
          check-language-support (or a fake list if in dryrun).
          List returned can be empty on success. None for failure.
         """
-        clsCommand = "check-language-support"
         # lang code may be separated by @, dot or spaces.
         # clsLang = lang.split('@')[0].split('.')[0].split(' ')[0]
         pattern = re.compile(r'([^.@\s]+)', re.IGNORECASE)
@@ -156,6 +157,10 @@ class ConfigureController(SubiquityController):
         snap_dir = snap_dir if snap_dir != '.' else '/'
         data_dir_base = "usr/share/language-selector"
         data_dir = os.path.join(snap_dir, data_dir_base)
+        # jammy does not (yet?) ship language-selector seeded.
+        # being defensive to prevent crashes.
+        clsCommand = "check-language-support"
+        envcp = None
         if not os.path.exists(data_dir):
             log.error("Language selector data dir %s seems not to be part"
                       " of the snap.", data_dir)
@@ -165,7 +170,12 @@ class ConfigureController(SubiquityController):
                 log.error("Cannot find language selector data directory.")
                 return None
 
-        cp = await arun_command([clsCommand, "-d", data_dir, "-l", clsLang])
+            # The env parameter is only needed if the package isn't in the snap
+            envcp = env
+            clsCommand = os.path.join("/usr/bin/", clsCommand)
+
+        cp = await arun_command([clsCommand, "-d", data_dir, "-l", clsLang],
+                                env=envcp)
         if cp.returncode != 0:
             log.error('Command "%s" failed with return code %d',
                       cp.args, cp.returncode)
@@ -186,7 +196,7 @@ class ConfigureController(SubiquityController):
         """ Install recommended packages.
         lang is expected to be one single language/locale.
         """
-        packages = await self.__recommended_language_packs(lang)
+        packages = await self.__recommended_language_packs(lang, env)
         # Hardcoded path is necessary to ensure escaping out of the snap env.
         aptCommand = "/usr/bin/apt"
         if packages is None: