Virtualenvs created by python3 itself don't have a pip executable installed, so use the pip module to install packages

Author: blag

Makefile

@@ -395,8 +395,8 @@ flake8: requirements .flake8
 	# NOTE We need to upgrade setuptools to avoid bug with dependency resolving in old versions
 	# Setuptools 42 added support for python_requires, which is used by the configparser package,
 	# which is required by the importlib-metadata package
-	$(VIRTUALENV_ST2CLIENT_DIR)/bin/pip install --upgrade "pip==$(PIP_VERSION)"
-	$(VIRTUALENV_ST2CLIENT_DIR)/bin/pip install --upgrade "setuptools==44.1.0"
+	$(VIRTUALENV_ST2CLIENT_DIR)/bin/python -m pip install --upgrade "pip==$(PIP_VERSION)"
+	$(VIRTUALENV_ST2CLIENT_DIR)/bin/python -m pip install --upgrade "setuptools==44.1.0"
 
 	$(VIRTUALENV_ST2CLIENT_DIR)/bin/activate; cd st2client ; ../$(VIRTUALENV_ST2CLIENT_DIR)/bin/python setup.py install ; cd ..
 	$(VIRTUALENV_ST2CLIENT_DIR)/bin/st2 --version
@@ -500,9 +500,9 @@ distclean: clean
 
 .PHONY: .requirements
 .requirements: virtualenv
-	$(VIRTUALENV_DIR)/bin/pip install --upgrade "pip==$(PIP_VERSION)"
+	$(VIRTUALENV_DIR)/bin/python -m pip install --upgrade "pip==$(PIP_VERSION)"
 	# Print out pip version
-	$(VIRTUALENV_DIR)/bin/pip --version
+	$(VIRTUALENV_DIR)/bin/python -m pip --version
 	# Generate all requirements to support current CI pipeline.
 	$(VIRTUALENV_DIR)/bin/python scripts/fixate-requirements.py --skip=virtualenv,virtualenv-osx -s st2*/in-requirements.txt contrib/runners/*/in-requirements.txt -f fixed-requirements.txt -o requirements.txt
 
@@ -525,23 +525,23 @@ requirements: virtualenv .requirements .sdist-requirements install-runners insta
 	@echo
 	# setuptools >= 41.0.1 is required for packs.install in dev envs
 	# setuptools >= 42     is required so setup.py install respects dependencies' python_requires
-	$(VIRTUALENV_DIR)/bin/pip install --upgrade "setuptools==44.1.0"
-	$(VIRTUALENV_DIR)/bin/pip install --upgrade "pbr==5.4.3"  # workaround for pbr issue
+	$(VIRTUALENV_DIR)/bin/python -m pip install --upgrade "setuptools==44.1.0"
+	$(VIRTUALENV_DIR)/bin/python -m pip install --upgrade "pbr==5.4.3"  # workaround for pbr issue
 
 	# Fix for Travis CI race
-	$(VIRTUALENV_DIR)/bin/pip install "six==1.12.0"
+	$(VIRTUALENV_DIR)/bin/python -m pip install "six==1.12.0"
 
 	# Fix for Travis CI caching issue
 	if [[ "$(TRAVIS_EVENT_TYPE)" != "" ]]; then\
-		$(VIRTUALENV_DIR)/bin/pip uninstall -y "pytz" || echo "not installed"; \
-		$(VIRTUALENV_DIR)/bin/pip uninstall -y "python-dateutil" || echo "not installed"; \
-		$(VIRTUALENV_DIR)/bin/pip uninstall -y "orquesta" || echo "not installed"; \
+		$(VIRTUALENV_DIR)/bin/python -m pip uninstall -y "pytz" || echo "not installed"; \
+		$(VIRTUALENV_DIR)/bin/python -m pip uninstall -y "python-dateutil" || echo "not installed"; \
+		$(VIRTUALENV_DIR)/bin/python -m pip uninstall -y "orquesta" || echo "not installed"; \
 	fi
 
 	# Install requirements
 	for req in $(REQUIREMENTS); do \
 		echo "Installing $$req..." ; \
-		$(VIRTUALENV_DIR)/bin/pip install $(PIP_OPTIONS) -r $$req ; \
+		$(VIRTUALENV_DIR)/bin/python -m pip install $(PIP_OPTIONS) -r $$req ; \
 	done
 
 	# Install st2common package to load drivers defined in st2common setup.py
@@ -553,7 +553,7 @@ requirements: virtualenv .requirements .sdist-requirements install-runners insta
 	# Note: We install prance here and not as part of any component
 	# requirements.txt because it has a conflict with our dependency (requires
 	# new version of requests) which we cant resolve at this moment
-	$(VIRTUALENV_DIR)/bin/pip install "prance==0.15.0"
+	$(VIRTUALENV_DIR)/bin/python -m pip install "prance==0.15.0"
 
 	# Install st2common to register metrics drivers
 	# NOTE: We pass --no-deps to the script so we don't install all the