Perform mount check after REST params valid on PUT

All the other methods (POST, GET, HEAD, DELETE and REPLICATE) first
validate the REST parameters and headers before performing the mount
check. Do the same for PUT.

Change-Id: I6e5f34cc65b57662b7f88224ca0e1501787e0f43
Signed-off-by: Peter Portante <peter.portante@redhat.com>