Remove DEBUG:....nsx_cluster:Attribute is empty or null

They serve no purpose, as if an important attribute is empty
or null and it shouldn't we'll know about it, and that's what
counts.

Change-Id: I7783cb6df76362d1b9b25b23f89a3a5d6df15406
Closes-bug: 1280500
Merge "Remove DEBUG:....nsx_cluster:Attribute is empty or null"