cli: Throw a warning during replace-brick

Change-Id: Ia024d055645ac2ec5cd506f2533831a159b38c20
BUG: 1039954
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/6559
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>