use string instead of ServiceState as key to map for GetServiceStatus

serviced service status hangs due to using jsonrpc instead of gob rpc:
  https://github.com/control-center/serviced/pull/874

DEMO:
```
NAME			ID				STATUS		UPTIME			HOST	DOCKER_ID	IN_SYNC
└─Zenoss.core		6fl86pf84ukireyru6gm57pyp									
  ├─localhost		3401mclpibaqcx0b4fmw4vvm3									
  │ ├─zenhub		3swabnlvtrwb39jpulnbml26x	Running		1m36.036149743s		plu-9	23c619fa1393	Y
  │ └─localhost		7xes29erwx1z3ff6ps8k2jlsd									
  │   ├─zenprocess	2ordfibkl6oidaaelaf8je4jw	Running		1m48.983957785s		plu-9	9dc8cd205fa0	Y
  │   ├─zencommand	421hzj8v5gvbatf89qpienva2	Running		1m50.173032798s		plu-9	43a2fc1678dc	Y
  │   ├─zenperfsnmp	4e4abgv8j4ezwq31yb19fn6mn	Running		1m45.782365934s		plu-9	d825725aa510	Y
  │   ├─collectorredis	5t2jltbqdhfrhlny513zkvqkg	Running		1m58.027526809s		plu-9	71fa4b795947	Y
  │   ├─zensyslog	6jnkouz02jegsj0arx9jstyio	Running		1m40.439498288s		plu-9	2e3b02c006d7	Y
  │   ├─zenpython	6mkpx977fbx0vzkl80hqpzzlh	Running		1m43.12413615s		plu-9	8b8aad2dc1a0	Y
  │   ├─zenstatus	7tw1rascahwq8ab8yh66cywdh	Running		1m40.564491811s		plu-9	ff551b87b65a	Y
  │   ├─zenmodeler	8ivoy5adtdv6l83p9y2orgttv	Running		1m52.889910618s		plu-9	f8d8c92129be	Y
  │   ├─zenjmx		9ozmbvy6e2ib88wqo8x2pr7kk	Running		1m44.43481383s		plu-9	aa55a0748083	Y
  │   ├─zenping		aenzrnk7w8lztx4z5vzogi4us	Running		1m51.424666297s		plu-9	79462f0bca24	Y
  │   ├─zentrap		ckoulhx4174ne8e0j1ylesdcz	Running		1m40.222652698s		plu-9	fe94367a04f2	Y
  │   └─MetricShipper	dyp1xln58mwsj3nbwtoszbu90	Running		1m47.849290353s		plu-9	2760429b4a17	Y
  ├─zproxy		3f5nmh86wgm45ge4ne64chkmg	Running		1m54.29069186s		plu-9	82343e9c376e	Y
  ├─zeneventd		3ph09i1ze70ioewj5zkwx6xgp	Running		2m0.389722506s		plu-9	5b93b80f2a27	Y
  ├─RabbitMQ		5ary0togxkvmkbpjpiycihak8	Running		1m24.138047366s		plu-9	be6b43671582	Y
  ├─MetricConsumer	8omhb3ka0k0kb9jeb5tgjqycu	Running		2m1.640401487s		plu-9	616364ad0abf	Y
  ├─Zope		a9znlytsdublewvkwmdoanp2p	Running		1m59.266388561s		plu-9	c56f634ff5d7	Y
  ├─opentsdb		as3dtcszqa1cql1ej3mdby4oa	Running		1m27.821253705s		plu-9	86c98f684208	Y
  ├─CentralQuery	axiec6j8abx0v5aecs78rw1sq	Running		1m31.616274569s		plu-9	7db36b715a95	Y
  ├─HBase		butyurrjp4nz3caka1m7rfmq1									
  │ ├─RegionServer	1649hmhd3tyv30s5k9h9o1qb1	Running		1m52.780428144s		plu-9	a34ed263b025	Y
  │ ├─ZooKeeper		3i4j78wwck0z9402s7am3ry4g	Running		1m33.065346997s		plu-9	cf89f0453231	Y
  │ └─HMaster		7coaj828b01fxuf0ysxzkz4wp	Running		1m47.166221933s		plu-9	e7341ca6b80a	Y
  ├─zenjobs		c2upqbae3w3taukgs1mv0lbgb	Running		1m57.946530625s		plu-9	367f9ca3c158	Y
  ├─zenactiond		d3jkx2swjxb8fytlz0dc01kb0	Running		1m34.318235235s		plu-9	9ec96e901b91	Y
  ├─zeneventserver	darar3sv7a269zjtbnhzvy5ih	Running		1m39.17016278s		plu-9	f6eec2692218	Y
  ├─MySQL		e06gpd5nocj4747i8mwypa1u	Running		1m40.981269338s		plu-9	97106e7bfdfb	Y
  └─redis		evqfi11f1sx1a449a5b0vleel	Running		1m56.338663467s		plu-9	9a33c9c69a63	Y

```