webadmin: Remove confusing coloring in VM interfaces widget

The gray color led people to believe the widget was disabled, so
changed it to black.

Change-Id: I2ffcf14f55b6b14ee62adde63987a2a3bae3cd6c
Bug-Url: https://bugzilla.redhat.com/1064431
Signed-off-by: Lior Vernia <lvernia@redhat.com>