Improves sssd.conf handling during ipa-client uninstall

The sssd.conf file is no longer left behind in case sssd was not
configured before the installation. However, the patch goes behind
the scope of this ticked and improves the handling of sssd.conf
during the ipa-client-install --uninstall in general.

The current behaviour (well documented in source code) is as follows:
  - In general, the IPA domain is simply removed from the sssd.conf
    file, instead of sssd.conf being rewritten from the backup. This
    preserves any domains added after installation.

  - If sssd.conf existed before the installation, it is restored to
    sssd.conf.bkp. However, any IPA domains from pre-installation
    sssd.conf should have been merged during the installation.

  - If sssd.conf did not exist before the installation, and no other
    domains than IPA domain exist in it, the patch makes sure that
    sssd.conf is moved to sssd.conf.deleted so user experiences no
    crash during any next installation due to its existence.

https://fedorahosted.org/freeipa/ticket/2740

ipapython/sysrestore.py

@@ -143,18 +143,26 @@ class FileStore:
                 break
         return result
 
-    def restore_file(self, path):
+    def restore_file(self, path, new_path = None):
         """Restore the copy of a file at @path to its original
         location and delete the copy.
 
+        Takes optional parameter @new_path which specifies the
+        location where the file is to be restored.
+
         Returns #True if the file was restored, #False if there
         was no backup file to restore
         """
 
-        root_logger.debug("Restoring system configuration file '%s'", path)
+        if new_path is None:
+            root_logger.debug("Restoring system configuration file '%s'", path)
+        else:
+            root_logger.debug("Restoring system configuration file '%s' to '%s'", path, new_path)
 
         if not os.path.isabs(path):
             raise ValueError("Absolute path required")
+        if new_path is not None and not os.path.isabs(new_path):
+            raise ValueError("Absolute new path required")
 
         mode = None
         uid = None
@@ -175,6 +183,9 @@ class FileStore:
             root_logger.debug("  -> Not restoring - '%s' doesn't exist", backup_path)
             return False
 
+        if new_path is not None:
+            path = new_path
+
         shutil.move(backup_path, path)
         os.chown(path, int(uid), int(gid))
         os.chmod(path, int(mode))