Use venv for base hub environment

- TLJH should support raspberry pi, which runs ARM. conda does
  not support ARM.
- Get nodejs from nodesource instead of conda or default repositories.
  Default repositories get out of date pretty quickly.
- Install CHP from npm

tests/test_installer.py

@@ -0,0 +1,10 @@
+"""
+Unit test  functions in installer.py
+"""
+from tljh import installer
+import os
+
+
+def test_ensure_node():
+    installer.ensure_node()
+    assert os.path.exists('/usr/bin/node')