Simplify AbstractSync

After porting scap and the rest of the sync-* scripts to use the
AbstractSync base class I realized that the implementation of
AbstractSync could be simplified by removing the _after_lock_aquire,
_local_sync and _phase_two_sync extension points. These were only used
by scap and the business logic was relatively easy to move into the
_before_cluster_sync and _after_cluster_sync methods.

Change-Id: Ibf853ada6566cde89edbcdb0865601fc90e6a674