Use our patched version of xunitmerge

The patched version of xunitmerge prioritizes non-skipped results
over skipped if there is a collision of test case's results with
the same name. The original version of xunitmerge doesn't use
test case's results and doesn't track collisions at all.

Correct merging requires that non-skipped results will not be
duplicated over input files.

Change-Id: I1db3daab7c37577e3be6bf694c1a58227f074928
Related-PROD: PROD-20207
diff --git a/tcp_tests/managers/k8smanager.py b/tcp_tests/managers/k8smanager.py
index 4a822d7..7476b60 100644
--- a/tcp_tests/managers/k8smanager.py
+++ b/tcp_tests/managers/k8smanager.py
@@ -608,7 +608,7 @@
         """
         with self.__underlay.remote(node_name=self.ctl_host) as r:
             cmd = ("apt-get install python-setuptools -y; "
-                   "pip install xunitmerge")
+                   "pip install git+https://github.com/mogaika/xunitmerge.git")
             LOG.debug('Installing xunitmerge')
             r.check_call(cmd)
             LOG.debug('Merging xunit')