After I found this problem appear in "volume unset",
I checked all the volume command and also found some
same problems. This patch fix them all.
The main reason of we ignored this problem before is
there was not any tests for it. So I add tests for
"nothing unset" for them all to test and aviod this
problem.
Also, I add unit tests for all snapshot commands
in volume v1 by the way in this patch. We will
need more tests to avoid some ignored problem.
Change-Id: I46775f24643d715e168b30785b8b531c0431a55b
Partial-bug: #1588588
fd876e4cc6