oe-selftest: export test results via xmlrunner

oe-selftest: export test results via xmlrunner

if available, use the xmlrunner for exporting the test results to a
dir named the same than the log where the text results are stored.
this means creating a dir with the name of the log (without the .log)
and dumping there the xml files that indicate the results of each of
the tests.

if xmlrunner is not available then it will behave the same as before,
no xml exports.

[YOCTO#9682]

Signed-off-by: Benjamin Esquivel <benjamin.esquivel@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>