core: use OsInfo instead of config value

Use OsInfo query instead of VirtIoScsiUnsupportedOsList config value:
* Added isOsSupportedForVirtIoScsi method to VmValidationUtils.
* Modified DiskValidator -> isOsSupportedForVirtIoScsi accordingly.
* Removed unused ConfigValues.VirtIoScsiUnsupportedOsList.

Change-Id: Idf434c5b7907f413399890a4b2e7d9f63f2bce9a
Signed-off-by: Daniel Erez <derez@redhat.com>