Add support for Redis replication

Implements a replication strategy for Redis.  The following
commands have been added to the Redis datastore manager:

create (with --replica_of and --replica_count arguments)
detach-replica
eject-replica-source
promote-to-replica-source

Unit tests were added, along with integration tests.

To run:
./redstack install
./redstack kick-start redis
(vi /etc/trove/test.conf and change volume_support to false)
./redstack int-tests --group=replication (or --group=redis_supported)

DocImpact: Documentation should reflect the newly supported
features for Redis (see above).

Depends-On: I633273d438c22f98bef2fd1535730bcdb5e5cff0
Change-Id: I2f0d53fe9049026faf1f37a40c1b5788abae4428
Implements: blueprint redis-replication

trove/common/cfg.py

@@ -564,8 +564,12 @@ redis_opts = [
                 'incremental, the runner will use the default full backup.',
                 deprecated_name='backup_incremental_strategy',
                 deprecated_group='DEFAULT'),
-    cfg.StrOpt('replication_strategy', default=None,
+    cfg.StrOpt('replication_strategy', default='RedisSyncReplication',
                help='Default strategy for replication.'),
+    cfg.StrOpt('replication_namespace',
+               default='trove.guestagent.strategies.replication.experimental.'
+                       'redis_sync',
+               help='Namespace to load replication strategies from.'),
     cfg.StrOpt('mount_point', default='/var/lib/redis',
                help="Filesystem path for mounting "
                "volumes if volume support is enabled."),