webadmin: Hide commands when specific provider is chosen

When a specific provider is chosen in the system tree, the add/remove
commands will now be hidden.

Change-Id: I27246a01e72fb70735888e38fcf5db3442cfba0d
Bug-Url: https://bugzilla.redhat.com/987999
Signed-off-by: Lior Vernia <lvernia@redhat.com>