Replace all occurances of LKGMCandidate with MasterSlave

LKGMCandidateSyncStage and LKGMCandidateSyncCompletionStage are
misleading names for the stages that we really use to synchronize commit
queue master/slaves. This CL refactors the names for clarity.

BUG=chromium:323293
TEST=Unit tests pass. Remote trybot with --buildbot --debug worked. Same
with --nobootstrap also worked.

Change-Id: Ic20ea868ff54cb6a743dba74a8ecde94b54b458c
Reviewed-on: https://chromium-review.googlesource.com/178100
Reviewed-by: David James <davidjames@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index b3d4240..1f4e26c 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -203,7 +203,7 @@
     raise NotImplementedError()
 
   def GetCompletionInstance(self):
-    """Returns the LKGMCandidateSyncCompletionStage for this build.
+    """Returns the MasterSlaveSyncCompletionStage for this build.
 
     Subclasses may override this method.
 
@@ -579,8 +579,8 @@
       sync_stage = self._GetStageInstance(stages.CommitQueueSyncStage)
       self.completion_stage_class = stages.CommitQueueCompletionStage
     elif cbuildbot_config.IsPFQType(self.build_config['build_type']):
-      sync_stage = self._GetStageInstance(stages.LKGMCandidateSyncStage)
-      self.completion_stage_class = stages.LKGMCandidateSyncCompletionStage
+      sync_stage = self._GetStageInstance(stages.MasterSlaveSyncStage)
+      self.completion_stage_class = stages.MasterSlaveSyncCompletionStage
     else:
       sync_stage = self._GetStageInstance(stages.ManifestVersionedSyncStage)
       self.completion_stage_class = stages.ManifestVersionedSyncCompletionStage