webadmin: Change label in Vm popup

The label "Run On:" in the VM popup host tab was changed into "Start
Running On:", which is more accurate description of the section.

Change-Id: I1890f6dbdc2fbc1f7af24116d821a79bb4ce021e
Bug-Url: https://bugzilla.redhat.com/958318
Signed-off-by: Ofri Masad <omasad@redhat.com>