[autotest] Add an option for label_cleaner

When -s option is enabled, label_cleaner checks if the server
where the tool is running on is 'primary' server.
If not, it just returns.

BUG=chromium:380365
TEST=Run the tool with/without -s option in local machine.
DEPLOY=apache

Change-Id: I0eb2c4463f94e51a96c81d3c02baae41fca025cd
Reviewed-on: https://chromium-review.googlesource.com/294878
Reviewed-by: Mungyung Ryu <mkryu@google.com>
Commit-Queue: Mungyung Ryu <mkryu@google.com>
Tested-by: Mungyung Ryu <mkryu@google.com>
diff --git a/frontend/afe/site_rpc_interface.py b/frontend/afe/site_rpc_interface.py
index 97ef017..a7cb19a 100644
--- a/frontend/afe/site_rpc_interface.py
+++ b/frontend/afe/site_rpc_interface.py
@@ -522,9 +522,10 @@
     shard.delete()
 
 
-def get_servers(role=None, status=None):
+def get_servers(hostname=None, role=None, status=None):
     """Get a list of servers with matching role and status.
 
+    @param hostname: FQDN of the server.
     @param role: Name of the server role, e.g., drone, scheduler. Default to
                  None to match any role.
     @param status: Status of the server, e.g., primary, backup, repair_required.
@@ -536,7 +537,7 @@
     if not server_manager_utils.use_server_db():
         raise error.RPCException('Server database is not enabled. Please try '
                                  'retrieve servers from global config.')
-    servers = server_manager_utils.get_servers(hostname=None, role=role,
+    servers = server_manager_utils.get_servers(hostname=hostname, role=role,
                                                status=status)
     return [s.get_details() for s in servers]