automation: workaround pip bug

The bug [1] in pip let the integrationtests fail on pyton 2.
The workaround is to use the previous pip version in tox.

[1]
  pypa/pip#8658

Change-Id: I2aa8747097dea7e8efd12e718409b8c7fa6d01a5
Signed-off-by: Dominik Holler <dholler@redhat.com>

automation/check-merged.sh

@@ -2,13 +2,14 @@
 
 if [ "$(rpm --eval "%dist"|cut -c2-4)" == "el7" ] ; then
     pip install --upgrade pip
+    export TOX_PIP_VERSION=20.1
     PIP=pip
     VARIANT=
 else
     PIP=pip-3
     VARIANT="3"
 fi
-$PIP install -U tox
+$PIP install -U tox tox-pip-version
 $PIP install -U requests-mock==1.5.2
 
 export PATH=/usr/local/bin:$PATH