Put overcloud state into testenv.json.

Sourcing devtest_overcloud is ugly, so like we did for undercloud,
turn it into a script we call that exports data itself.

Change-Id: If7705f15741e9e63ec1ef8759710e9e664bdad97
Stop editing config.json.

Now that the t-i-e element supports reading local.json in preference
to config.json, we can put our edited state in local.json and avoid
dirtying the git tree.

Change-Id: Iecbc4f379710242f4355e2f8c4050fc2edc7dd06
Merge "Put overcloud state into testenv.json."
Merge "Stop editing config.json."