Add two variants of make targets for e2e-tests

The default one 'test-e2e' starts with a clean slate ie. it removes
existing virtualenvs and sets them up again before running the tests.

The 'test-e2e-quick' reuses the existing virtualenvs (and hence runs
faster).

Also updated README.

Makefile

@@ -2,6 +2,8 @@
 
 TOX_ENV ?= py36
 
+E2E_PYTHON_EXE ?= python3.6
+
 clean:
 	find . -name '*.pyc' -exec rm -f {} +
 	find . -name '*.pyo' -exec rm -f {} +
@@ -23,6 +25,12 @@ test-tox-all:
 	tox
 
 test-e2e:
+	rm -rf tests/profiles/*/.env_$(E2E_PYTHON_EXE)*
+	cd tests && ./e2e-tests webapp
+	cd tests && ./e2e-tests conflicting
+	cd tests && ./e2e-tests cyclic
+
+test-e2e-quick:
 	cd tests && ./e2e-tests webapp
 	cd tests && ./e2e-tests conflicting
 	cd tests && ./e2e-tests cyclic

README.rst

@@ -391,6 +391,23 @@ are released, these need to be updated. At present the process is
 manual but I have plans to setup nightly builds for these for faster
 feedback.
 
+The end-to-end tests can be run as follows,
+
+.. code-block:: bash
+
+    $ make test-e2e  # starts with a clean virtualenvs
+
+    $ # or
+
+    $ make test-e2e-quick # reuses existing virtualenvs
+
+By default the e2e tests uses python executable ``python3.6``. To use
+an alternate version set the environment var ``E2E_PYTHON_EXE``.
+
+.. code-block:: bash
+
+    $ E2E_PYTHON_EXE=python2.7 make test-e2e
+
 
 Release checklist
 -----------------