Add abililty to use system python

Moving virtual environments between systems is problematic... and
unnecessary when creating container images. These modifications allow
the ability to install app dependencies into the system python, and use
that instead of a virtual environment.

script/test

@@ -1,12 +1,23 @@
 #!/bin/bash
 
+# script/test: Run static code checks and unit tests
+
 # If a command fails, exit the script
 set -e
 
 # Ensure we are in the app root directory (not the /script directory)
 cd "$(dirname "${0}")/.."
 
-pipenv run pylint app.py atst/ tests/
+if [ -z "${SKIP_PIPENV+xxxx}" ]; then
+  CMD_PREFIX='pipenv run '
+fi
+PYLINT_CMD="${CMD_PREFIX}pylint"
+PYTHON_CMD="${CMD_PREFIX}python"
+
+# Run lint check
+echo "Running lint..."
+${PYLINT_CMD} app.py atst/ tests/
 
 # Run unit tests
-pipenv run python -m pytest -s $*
+echo "Running unit tests..."
+${PYTHON_CMD} -m pytest -s $*