Lxd instance not found fix false positives (#7521)

* lxd: Add lxc command execution debug statement.

* lxd: avoid false positives in "instance not found" detection

Due to changes over time in the error message which lxd printed when an
instance wasn't found, the detection logic in the lxd connection plugin
matched any "not found" string.  Unfortunately this also false triggered
on other errors e.g. "/usr/bin/python3: not found" from the payload,
giving a confusing error message "UNREACHABLE! ... instance not found"
to the ansible user.

* Update changelog fragment.

---------

Co-authored-by: Felix Fontein <felix@fontein.de>

changelogs/fragments/lxd-instance-not-found-avoid-false-positives.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - "lxd connection plugin - tighten the detection logic for lxd ``Instance not found`` errors, to avoid false detection on unrelated errors such as ``/usr/bin/python3: not found`` (https://github.com/ansible-collections/community.general/pull/7521)."

plugins/connection/lxd.py

@@ -101,6 +101,8 @@ class Connection(ConnectionBase):
             self.get_option("executable"), "-c", cmd
         ])
 
+        self._display.vvvvv(u"EXEC {0}".format(local_cmd), host=self._host())
+
         local_cmd = [to_bytes(i, errors='surrogate_or_strict') for i in local_cmd]
         in_data = to_bytes(in_data, errors='surrogate_or_strict', nonstring='passthru')
 
@@ -110,10 +112,12 @@ class Connection(ConnectionBase):
         stdout = to_text(stdout)
         stderr = to_text(stderr)
 
+        self._display.vvvvv(u"EXEC lxc output: {0} {1}".format(stdout, stderr), host=self._host())
+
         if "is not running" in stderr:
             raise AnsibleConnectionFailure("instance not running: %s" % self._host())
 
-        if "not found" in stderr:
+        if stderr.strip() == "Error: Instance not found" or stderr.strip() == "error: not found":
             raise AnsibleConnectionFailure("instance not found: %s" % self._host())
 
         return process.returncode, stdout, stderr