domaincapstest: Use proper input file based on 'variant' in 'fillQemuCaps'

domaincapstest: Use proper input file based on 'variant' in 'fillQemuCaps'

The qemu part of 'domaincapstest' supports testing of the '+hvf' variant
of files, but doesn't properly pick the input file. The input file lacks
the variant part thus the wrong file is used.

Propagate the variant and select the correct input file.

Fixes: 738c5bae888cfa72ed359899cf1a41fed9dbb0f5
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>