engine: Cache spice support for os/compatibility version

Patch 31903bda17f97c2d785238b3d0d557d3c24f40b9 introduced detection of
spice support on OSs and compatibility version. This detection
implemented as an async query to OsRepository. This query is called from
updateActionAvailability but the design requires the calls to be
synchronous. This patch introduces caching spice support depending on
all OSs and compatibility versions.

Change-Id: Ib97d68ccd0d30fd07e8d1a7d1322f731aef220f7
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/998705