make `weave status` fail when weave isn't running but still always show weavedns status, if present
make `weave status` fail when weave isn't running
but still always show weavedns status, if present

Closes #784.

tomwilkie/weave,dpw/weave,OnePaaS/weave,bboreham/weave,tomwilkie/weave,awanke/weave,inercia/weave,n054/weave,beni55/weave,errordeveloper/weave,2opremio/weave,aaam/weave,awanke/weave,aaam/weave,narry/weave,awh/weave,narry/weave,squaremo/weave,dpw/weave,rade/weave,paulbellamy/weave,paladin74/weave,squaremo/weave,kidaa/weave,weaveworks/weave,achanda/weave,2opremio/weave,awanke/weave,squaremo/weave,rade/weave,kidaa/weave,achanda/weave,OnePaaS/weave,cgvarela/weave,achanda/weave,paladin74/weave,2opremio/weave,beni55/weave,philipz/weave,weaveworks/weave,n054/weave,beni55/weave,awanke/weave,errordeveloper/weave,awh/weave,dpw/weave,rade/weave,BWITS/weave,errordeveloper/weave,philipz/weave,rade/weave,squaremo/weave,ycaihua/weave,weaveworks/weave,dpw/weave,squaremo/weave,achanda/weave,awanke/weave,kidaa/weave,ycaihua/weave,ycaihua/weave,tomwilkie/weave,awh/weave,achanda/weave,bboreham/weave,ycaihua/weave,cgvarela/weave,inercia/weave,paulbellamy/weave,philipz/weave,kidaa/weave,narry/weave,2opremio/weave,BWITS/weave,aaam/weave,tomwilkie/weave,kidaa/weave,paulbellamy/weave,paulbellamy/weave,n054/weave,BWITS/weave,bboreham/weave,awh/weave,narry/weave,weaveworks/weave,OnePaaS/weave,OnePaaS/weave,BWITS/weave,OnePaaS/weave,cgvarela/weave,dpw/weave,rade/weave,cgvarela/weave,n054/weave,inercia/weave,inercia/weave,philipz/weave,tomwilkie/weave,2opremio/weave,errordeveloper/weave,beni55/weave,paladin74/weave,n054/weave,aaam/weave,inercia/weave,bboreham/weave,errordeveloper/weave,paladin74/weave,beni55/weave,paladin74/weave,ycaihua/weave,philipz/weave,cgvarela/weave,bboreham/weave,awh/weave,narry/weave,aaam/weave,BWITS/weave