Workaround long shebang issue

Sometimes tox gate experiences issue [1] with the
shebang length which is currently limited to
the 127 symbols.

As a workaround for that pip can be called
as the python module with 'python -m pip [...]'

RHOSINFRA-1475
[1] pypa/pip#1773

Change-Id: I9144c476341de1fc670dd5cead30f52cb6b274fc

tox.ini

@@ -37,13 +37,13 @@ whitelist_externals =
 # This must work for both cases: installing with/without --upgrade
 deps =
 commands =
-     bash -c "PIP_LOG={envdir}/log/pip-conflicts-1.log pip install -q 'pip>=9.0.1'"
-     - pip check
-     bash -c "PIP_LOG={envdir}/log/pip-conflicts-2.log pip install -q -e ."
-     pip check
-     bash -c "PIP_LOG={envdir}/log/pip-conflicts-3.log pip uninstall -q -y infrared"
-     bash -c "PIP_LOG={envdir}/log/pip-conflicts-4.log pip install -q --upgrade -e ."
-     pip check
+     bash -c "PIP_LOG={envdir}/log/pip-conflicts-1.log python -m pip install -q 'pip>=9.0.1'"
+     - python -m pip check
+     bash -c "PIP_LOG={envdir}/log/pip-conflicts-2.log python -m pip install -q -e ."
+     python -m pip check
+     bash -c "PIP_LOG={envdir}/log/pip-conflicts-3.log python -m pip uninstall -q -y infrared"
+     bash -c "PIP_LOG={envdir}/log/pip-conflicts-4.log python -m pip install -q --upgrade -e ."
+     python -m pip check
 
 [testenv:pep8]
 # hacking pulls flake8, pep8 and more https://pypi.org/project/hacking/
@@ -124,7 +124,7 @@ commands = bash -c 'cd docs; make clean; make html'
 deps = {toxinidir}
 setenv =
     PIP_LOG={envdir}/log/pip-cli.log
-install_command = pip install -q --retries 10 {packages}
+install_command = python -m pip install -q --retries 10 {packages}
 commands = infrared plugin add all
 
 [testenv:plugin-registry]