Added test_vm_discovery.py

1. Added cfme/tests/infrastructure/test_vm_discovery.py
Tests whether cfme will discover a vm change (add/delete) without being manually refreshed

2. Implemented version.pick() for the name of the 'Archive' tree element in the navigation menu (using updated key for downstream)
Merge pull request #847 from slouderm/test_vm_discovery

Test vm discovery