CLI: Show warning message only for remove-brick commit

Earlier warning message for checking the removed-bricks for
any unmigrated files was thrown both for remove-brick commit
and force.

With this change the warning message will be shown only for
remove-brick commit.

Change-Id: Ib1fa47d831d5189088c77c5cf709a25ff36d7379
BUG: 1157974
Signed-off-by: Susant Palai <spalai@redhat.com>
Reviewed-on: http://review.gluster.org/8983
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>