Add three tests for minion_id generation

These tests are in response to a regression fixed a couple days ago, where when /etc/hosts needs to be parsed to determine the minion_id and the file contains a blank line, an exception is raised. The following three methods of determining the minion_id are tested:

1. Calling ``socket.getfqdn()``
2. Checking ``/etc/hostname``
3. Parsing ``/etc/hosts``