added to CLI: serviced docker sync to push all unique images used by ser...

...vices to local registry

DEMO:
```
# plu@plu-9: serviced service list |grep Zenoss
  Zenoss.core		anai9vxxporc1c22b5ct9nex2	0					default		1	auto	HBase

# plu@plu-9: docker images |grep anai9vxxporc1c22b5ct9nex2
plu-9:5000/anai9vxxporc1c22b5ct9nex2/devimg     latest              33a12f6ffe58        6 days ago          3.329 GB
plu-9:5000/anai9vxxporc1c22b5ct9nex2/hbase      latest              4a01c657faa4        2 weeks ago         560.9 MB
plu-9:5000/anai9vxxporc1c22b5ct9nex2/opentsdb   latest              ca43a978631e        7 weeks ago         1.386 GB

# plu@plu-9: ./serviced docker sync
Syncing image to local docker registry: plu-9:5000/anai9vxxporc1c22b5ct9nex2/devimg ...
Syncing image to local docker registry: plu-9:5000/anai9vxxporc1c22b5ct9nex2/opentsdb ...
Syncing image to local docker registry: plu-9:5000/anai9vxxporc1c22b5ct9nex2/hbase ...
images synced to local docker registry
```