Allow including hivemind entry points to modules

Example module definition.

[hivemind.modules]
iptables = hivemind_contrib.iptables

Change-Id: I0fcedbcf5eec47b3c0a93215a900d8add8420c2e
Moved some services out to hivemind_contrib

The hivemind_contrib repository is located at
git clone git@github.com:NeCTAR-RC/hivemind_contrib.git

Change-Id: Iea72a8ed35cc700fde097aa30ecc97de4c341c20
Default arguments to environment values

Change-Id: If9650f6464fff6a6c3c897526e5a82b19e57c7ba
Merge "Allow including hivemind entry points to modules"
Merge topic 'rebased'

* changes:
  Default arguments to environment values
  Moved some services out to hivemind_contrib