Change k8s xunitmerge reporter download link

Sometimes pip install with git+https protocol can fail with
"curl transfer closed with outstanding read data remaining" error.
Downloading of archive files instead of repo clonning also much
faster.

Change-Id: Iffa7cff23f1182576cafafd33ad4d1783b1194d9
diff --git a/tcp_tests/managers/k8smanager.py b/tcp_tests/managers/k8smanager.py
index 38521c7..5c71285 100644
--- a/tcp_tests/managers/k8smanager.py
+++ b/tcp_tests/managers/k8smanager.py
@@ -630,7 +630,8 @@
         """
         with self.__underlay.remote(node_name=self.ctl_host) as r:
             cmd = ("apt-get install python-setuptools -y; "
-                   "pip install git+https://github.com/mogaika/xunitmerge.git")
+                   "pip install "
+                   "https://github.com/mogaika/xunitmerge/archive/master.zip")
             LOG.debug('Installing xunitmerge')
             r.check_call(cmd, raise_on_err=False)
             LOG.debug('Merging xunit')