webadmin: Renamed the Close button with Cancel

Renamed the Close button with Cancel in the commit remove bricks dialog.

Change-Id: I0adefcc0137ed51927a4f61264d6c31bc475bdef
Bug-Url: https://bugzilla.redhat.com/1024817
Signed-off-by: Shubhendu Tripathi <shtripat@redhat.com>