fixes ZEN-13575: only pause/resume services that have Snapshot.(Pause|Re...

...sume) defined

DEMO:
```
# plu@plu-9: serviced service status 
NAME			ID				STATUS		UPTIME		HOST	DOCKER_ID
└─Zenoss.core		swcbene230d5rp91k8czk0y9						
  ├─opentsdb		16vpyf77lg2g93bk5n9srm1g7						
  │ ├─reader		azsl9g2xlydqtibhfebqjqxcs	Stopped					
  │ └─writer		bl31f85c179ewur3mg2p1redx	Stopped					
  ├─zeneventserver	1nn16n30expakpd3zfdn5znh8	Running		41.958639147s	plu-9	97af521d7743
  ├─redis		3dbqulbcj0yw1f1ucj4dkp50m	Running		59.904882554s	plu-9	d30ae161db9c
  ├─zenjobs		5c1bz728iim65duq5c2qqmohi	Stopped					
  ├─MetricConsumer	5o9ozlh7102hqlltxhgxeirbe	Stopped					
  ├─MySQL		5wto1vktlr29xyvx70raxp6o8	Running		53.000211858s	plu-9	b4c701a46e88
  ├─HBase		8zb4whzmeeybll6jr0qnrb6hs						
  │ ├─HMaster		51vh0eiqtvbibkegii0jkaju2	Stopped					
  │ ├─ZooKeeper		6qahmolqmdd5rhnrqkxbu603k	Stopped					
  │ └─RegionServer	9t9b1vyc1nrt77le4291fjkil	Stopped					
  ├─CentralQuery	94r85ozdgbeglk07x3w6gxveh	Stopped					
  ├─Zope		9lbhggb2vsbtu53s3salqwa7q	Stopped					
  ├─RabbitMQ		9ubqpbd7e9mdgj3cqahbvvt9p	Running		47.453365213s	plu-9	ae6ae8f1ccba
  ├─zenactiond		9xuyy407wxlhvn8rdic509jwp	Stopped					
  ├─memcached		aujvalerz75nxcn1sygplhy52	Running		59.380924809s	plu-9	6bc7b2e7f639
  ├─zeneventd		bn1kpqxpq1304zbxgae07qvce	Stopped					
  ├─localhost		crerare6hipg86xc9kiwmiodl						
  │ ├─localhost		7sm5uoipbefewlutobjibuz4z						
  │ │ ├─MetricShipper	2adevaa42e0yt98bazis3d3r0	Stopped					
  │ │ ├─zenmodeler	5gl1fy2t540bk2ffh5ue3djjs	Stopped					
  │ │ ├─zenperfsnmp	5ojhsl9kxreq8uye4l9zspu5t	Stopped					
  │ │ ├─zenprocess	7r8mbhvubipzprg6192vpmyk5	Stopped					
  │ │ ├─zencommand	9m4xl0uoe9ek24piua2l270jx	Stopped					
  │ │ ├─zenstatus	bbf3zkjv15niexpk5l867twin	Stopped					
  │ │ ├─zenping		blye38xictugvatddi55nxhbg	Stopped					
  │ │ ├─zentrap		c6geufxfzes92rg72ovkgvp6f	Stopped					
  │ │ ├─collectorredis	cb021jricdcpqmufkcuvlvtfq	Stopped					
  │ │ ├─zenpython	d1bvtmmihefet0b0t38xzpz95	Stopped					
  │ │ ├─zensyslog	e54p2d839ako9sirq6alx6e9f	Stopped					
  │ │ └─zenjmx		iyh4tznvs3qagk12mmcnrlkm	Stopped					
  │ └─zenhub		af85cyggoub38qaqk7e87l1pw	Stopped					
  ├─zproxy		cyh8hdd97itc18angx7w3xfq0	Stopped					
  └─Zauth		q0xc7l890huatuoqagvgco4r	Stopped					

# plu@plu-9: serviced service run Zope zenpack install dist/ZenPacks.zenoss.AdvancedSearch-1.1.3-py2.7.egg
...
2014-08-12 21:33:24,769 INFO zen.HookReportLoader: Loading reports from /opt/zenoss/ZenPacks/ZenPacks.zenoss.AdvancedSearch-1.1.3-py2.7.egg/ZenPacks/zenoss/AdvancedSearch/reports
I0812 15:33:30.998450 17765 shell.go:201] Committing container

# plu@plu-9: serviced service status 
NAME			ID				STATUS		UPTIME			HOST	DOCKER_ID
└─Zenoss.core		swcbene230d5rp91k8czk0y9							
  ├─opentsdb		16vpyf77lg2g93bk5n9srm1g7							
  │ ├─reader		azsl9g2xlydqtibhfebqjqxcs	Stopped						
  │ └─writer		bl31f85c179ewur3mg2p1redx	Stopped						
  ├─zeneventserver	1nn16n30expakpd3zfdn5znh8	Running		3m46.520680049s		plu-9	97af521d7743
  ├─redis		3dbqulbcj0yw1f1ucj4dkp50m	Running		4m4.585036238s		plu-9	d30ae161db9c
  ├─zenjobs		5c1bz728iim65duq5c2qqmohi	Stopped						
  ├─MetricConsumer	5o9ozlh7102hqlltxhgxeirbe	Stopped						
  ├─MySQL		5wto1vktlr29xyvx70raxp6o8	Running		3m57.621875094s		plu-9	b4c701a46e88
  ├─HBase		8zb4whzmeeybll6jr0qnrb6hs							
  │ ├─HMaster		51vh0eiqtvbibkegii0jkaju2	Stopped						
  │ ├─ZooKeeper		6qahmolqmdd5rhnrqkxbu603k	Stopped						
  │ └─RegionServer	9t9b1vyc1nrt77le4291fjkil	Stopped						
  ├─CentralQuery	94r85ozdgbeglk07x3w6gxveh	Stopped						
  ├─Zope		9lbhggb2vsbtu53s3salqwa7q	Stopped						
  ├─RabbitMQ		9ubqpbd7e9mdgj3cqahbvvt9p	Running		3m52.045029555s		plu-9	ae6ae8f1ccba
  ├─zenactiond		9xuyy407wxlhvn8rdic509jwp	Stopped						
  ├─memcached		aujvalerz75nxcn1sygplhy52	Running		4m4.031951724s		plu-9	6bc7b2e7f639
  ├─zeneventd		bn1kpqxpq1304zbxgae07qvce	Stopped						
  ├─localhost		crerare6hipg86xc9kiwmiodl							
  │ ├─localhost		7sm5uoipbefewlutobjibuz4z							
  │ │ ├─MetricShipper	2adevaa42e0yt98bazis3d3r0	Stopped						
  │ │ ├─zenmodeler	5gl1fy2t540bk2ffh5ue3djjs	Stopped						
  │ │ ├─zenperfsnmp	5ojhsl9kxreq8uye4l9zspu5t	Stopped						
  │ │ ├─zenprocess	7r8mbhvubipzprg6192vpmyk5	Stopped						
  │ │ ├─zencommand	9m4xl0uoe9ek24piua2l270jx	Stopped						
  │ │ ├─zenstatus	bbf3zkjv15niexpk5l867twin	Stopped						
  │ │ ├─zenping		blye38xictugvatddi55nxhbg	Stopped						
  │ │ ├─zentrap		c6geufxfzes92rg72ovkgvp6f	Stopped						
  │ │ ├─collectorredis	cb021jricdcpqmufkcuvlvtfq	Stopped						
  │ │ ├─zenpython	d1bvtmmihefet0b0t38xzpz95	Stopped						
  │ │ ├─zensyslog	e54p2d839ako9sirq6alx6e9f	Stopped						
  │ │ └─zenjmx		iyh4tznvs3qagk12mmcnrlkm	Stopped						
  │ └─zenhub		af85cyggoub38qaqk7e87l1pw	Stopped						
  ├─zproxy		cyh8hdd97itc18angx7w3xfq0	Stopped						
  └─Zauth		q0xc7l890huatuoqagvgco4r	Stopped	

================== serviced.log:
I0812 15:33:31.402228 13202 filesystem.go:162] Mounting vfs:rsync tenantId:swcbene230d5rp91k8czk0y9 baseDir:/tmp/serviced-root/var/volumes/default
I0812 15:33:31.892055 13202 host.go:264] Pausing service instance 7aruh1b50m7ucbjsyjqr7grji for service redis (3dbqulbcj0yw1f1ucj4dkp50m)
I0812 15:33:32.981294 13202 host.go:264] Pausing service instance 3ktqxnfbheeqtvxdsfn0mw869 for service memcached (aujvalerz75nxcn1sygplhy52)
I0812 15:33:34.068174 13202 host.go:264] Pausing service instance a00c5rqzlxem9qv02csv49jy1 for service MySQL (5wto1vktlr29xyvx70raxp6o8)
I0812 15:33:37.170779 13202 host.go:264] Pausing service instance eag05lau2synifwog2pus1l5z for service RabbitMQ (9ubqpbd7e9mdgj3cqahbvvt9p)
I0812 15:33:44.319771 13202 host.go:264] Pausing service instance 4uol79xvja2y5uek3kafcupzw for service zeneventserver (1nn16n30expakpd3zfdn5znh8)
I0812 15:33:45.339931 13202 filesystem.go:162] Mounting vfs:rsync tenantId:swcbene230d5rp91k8czk0y9 baseDir:/tmp/serviced-root/var/volumes/default
I0812 15:33:45.340013 13202 dfs.go:135] DistributedFileSystem.Snapshot service=swcbene230d5rp91k8czk0y9 label=swcbene230d5rp91k8czk0y9_20140812-203345 volume={Conn:0xc2097a63c0}
I0812 15:33:45.340125 13202 rsync.go:111] Performing snapshot rsync command: /usr/bin/rsync [-a /tmp/serviced-root/var/volumes/default/swcbene230d5rp91k8czk0y9/ /tmp/serviced-root/var/volumes/default/swcbene230d5rp91k8czk0y9_20140812-203345/]
I0812 15:33:47.998496 13202 dfs.go:167] Successfully created snapshot for service Id:swcbene230d5rp91k8czk0y9 Name:Zenoss.core Label:swcbene230d5rp91k8czk0y9_20140812-203345
```