tests: More output options for xml2xml tests

tests: More output options for xml2xml tests

So far, qemuxml2xml test was only able to check if the result matches
the original or the appropriate XML in qemuxml2xmloutdata regardless on
flags used to format the XML. Since the result can be different
depending on VIR_DOMAIN_XML_INACTIVE flag being used or not, this patch
adds support for qemuxml2xmlout-%s-active.xml and
qemuxml2xmlout-%s-inactive.xml output files. If the file specific to the
flag used exists, it is used in preference to the generic
qemuxml2xmlout-%s.xml file when reading the expected output.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>