Refactor authconfig use in ipa-client-install

When certain features are being configured via authconfig, we need to
remember what was configured and what was the state before it so that
during uninstall we restore proper state of the services.

Mostly it affects sssd configuration with multiple domains but also
pre-existing LDAP and krb5 configurations.

This should fix following tickets:
https://fedorahosted.org/freeipa/ticket/1750
https://fedorahosted.org/freeipa/ticket/1769

ipapython/sysrestore.py

@@ -130,6 +130,19 @@ class FileStore:
         self.files[filename] = string.join([str(stat.st_mode),str(stat.st_uid),str(stat.st_gid),path], ',')
         self.save()
 
+    def has_file(self, path):
+        """Checks whether file at @path was added to the file store
+
+        Returns #True if the file exists in the file store, #False otherwise
+        """
+        result = False
+        for (key, value) in self.files.items():
+            (mode,uid,gid,filepath) = string.split(value, ',', 3)
+            if (filepath == path):
+                result = True
+                break
+        return result
+
     def restore_file(self, path):
         """Restore the copy of a file at @path to its original
         location and delete the copy.