Use GCM sink if SINK=gcm is specified.
Use GCM sink if SINK=gcm is specified.

Default is influxdb which mirrors today's behavior.

Fixes #117.

saiwl/heapster,piosz/heapster,vicki-c/heapster,saiwl/heapster,jszczepkowski/heapster,digideskio/heapster,shilpamayanna/heapster,vishh/heapster-1,mdshuai/heapster,jackzampolin/heapster,nlamirault/heapster,mwielgus/heapster,shilpamayanna/heapster,apeeyush/heapster,taimir/heapster,nlamirault/heapster,saad-ali/heapster,thucatebay/heapster,piosz/heapster,a-robinson/heapster,burmanm/heapster,Huawei-PaaS/heapster,jszczepkowski/heapster,huangyuqi/heapster,afein/heapster,wulonghui/heapster,ravihansa3000/heapster,jfoy/heapster,mdshuai/heapster,AlmogBaku/heapster,afein/heapster,adfin/statster,johanneswuerbach/heapster,a-robinson/heapster,jimmidyson/heapster,titilambert/heapster,saad-ali/heapster,aegixx/heapster,jimmidyson/heapster,liubog2008/heapster,apeeyush/heapster,liuhewei/heapster,relh/heapster,mwringe/heapster,Huawei-PaaS/heapster,bruceauyeung/heapster,mwielgus/heapster,digideskio/heapster,luxas/heapster,liuhewei/heapster,dalanlan/heapster,lavalamp/heapster,skytap/heapster,skytap/heapster,Stackdriver/heapster,thucatebay/heapster,luxas/heapster,adfin/statster,bluebreezecf/heapster,jackzampolin/heapster,wulonghui/heapster,ravihansa3000/heapster,krzyzacy/heapster,jfoy/heapster,naxhh/heapster,dalanlan/heapster,taimir/heapster,johanneswuerbach/heapster,fzu-huang/heapster,fzu-huang/heapster,andyxning/heapster,mwringe/heapster,lavalamp/heapster,AlmogBaku/heapster,titilambert/heapster,andyxning/heapster,burmanm/heapster,Stackdriver/heapster,bluebreezecf/heapster,relh/heapster,bruceauyeung/heapster,whuwxl/heapster,vicki-c/heapster,liubog2008/heapster,vishh/heapster-1,huangyuqi/heapster,whuwxl/heapster,naxhh/heapster,aegixx/heapster,krzyzacy/heapster