install: Call hostnamectl set-hostname only if --hostname option is used

This commit also splits hostname backup and configuration into two separate
functions. This allows us to backup hostname without setting it at the
same time.

https://fedorahosted.org/freeipa/ticket/6071

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipaplatform/base/tasks.py

@@ -45,14 +45,11 @@ class BaseTaskNamespace(object):
 
         raise NotImplementedError()
 
-    def backup_and_replace_hostname(self, fstore, statestore, hostname):
+    def backup_hostname(self, fstore, statestore):
         """
         Backs up the current hostname in the statestore (so that it can be
         restored by the restore_hostname platform task).
 
-        Makes sure that new hostname (passed via hostname argument) is set
-        as a new pemanent hostname for this host.
-
         No return value expected.
         """
 
@@ -109,7 +106,7 @@ class BaseTaskNamespace(object):
     def restore_hostname(self, fstore, statestore):
         """
         Restores the original hostname as backed up in the
-        backup_and_replace_hostname platform task.
+        backup_hostname platform task.
         """
 
         raise NotImplementedError()

ipaplatform/redhat/tasks.py

@@ -332,22 +332,13 @@ class RedHatTaskNamespace(BaseTaskNamespace):
 
         return result
 
-    def backup_and_replace_hostname(self, fstore, statestore, hostname):
-        old_hostname = socket.gethostname()
-        try:
-            self.set_hostname(hostname)
-        except ipautil.CalledProcessError as e:
-            root_logger.debug(traceback.format_exc())
-            root_logger.error(
-                "Failed to set this machine hostname to %s (%s).",
-                old_hostname, e
-            )
-
+    def backup_hostname(self, fstore, statestore):
         filepath = paths.ETC_HOSTNAME
         if os.path.exists(filepath):
             fstore.backup_file(filepath)
 
         # store old hostname
+        old_hostname = socket.gethostname()
         statestore.backup_state('network', 'hostname', old_hostname)
 
     def restore_hostname(self, fstore, statestore):