Add some unit tests to the node and swarm cli code

Start work on adding unit tests to our cli code in order to have to
write less costly integration test.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

command/node/testdata/node-inspect-pretty.simple.golden

@@ -0,0 +1,23 @@
+ID:			nodeID
+Name:			defaultNodeName
+Labels:
+ - lbl1 = value1
+Hostname:		defaultNodeHostname
+Joined at:		2009-11-10 23:00:00 +0000 utc
+Status:
+ State:			Ready
+ Availability:		Active
+ Address:		127.0.0.1
+Platform:
+ Operating System:	linux
+ Architecture:		x86_64
+Resources:
+ CPUs:			0
+ Memory:		20 MiB
+Plugins:
+  Network:		bridge, overlay
+  Volume:		local
+Engine Version:		1.13.0
+Engine Labels:
+ - engine = label
+