backend: GetoVirtISOsQuery use RpmVersionUtils

- Replace parseIsoFileVersion() by direct RpmVersion call
- Use RpmVersionUtils for isIsoVersionSupported()

Change-Id: I17cae0eed9e6109fa0c7efb460e02ab7073fe21d
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>