Required some rewiring in inventory code to make sure we're using
the DataLoader class for some data file operations, which makes mocking
them much easier.
Also identified two corner cases not currently handled by the code, related
to inventory variable sources and which one "wins". Also noticed we weren't
properly merging variables from multiple group/host_var file locations
(inventory directory vs. playbook directory locations) so fixed as well.
Note that this test was broken in devel because it was really just
duplicating the AES256 test because setting v.cipher_name to 'AES'
no longer selected AES after it was de-write-whitelisted.
Now that we've removed the VaultAES encryption code, we embed static
output from an earlier version and test that we can decrypt it.
