UI: datacenter/cluster running on host behavior

When changing datacenter/cluster we need to fall back to "run on any
host" selection and not stay with "run on specific host" if it was
previously selected.

Change-Id: I5ca584e0c98a4e9d3823b0333b92bff93db20872
Bug-Url: https://bugzilla.redhat.com/1136228
Signed-off-by: Shahar Havivi <shaharh@redhat.com>