proxyquery: add docstring to _make_exec_requests

It's a simple docstring; it just specifies the expected inputs and
outputs.
proxyquery: factor source header processing

This block is now in a separate function, in order to reduce the overall
size and complexity of `post_job`.
proxyquery: rename cluster config loading funcs
proxyquery: simplify and refactor post_job
Move a ClusterConfigParser method to ZvmNode

`get_list_of_remote_objects` operates only on a ZvmNode, and it seems
more appropriate to just make it an instance method of ZvmNode.
proxyquery: encapsulate cluster config parsing
proxyquery: remove a redundant variable
configparser: fix a pep8 error
proxyquery: add comments to the code

Because there aren't very many.
requirements.txt: fix swift pkg search page

Something changed with the Swift release on Launchpad, so you no longer
find a >=2.0.0 package on launchpad.net/swift.

This was causing package installs to fail.
Merge pull request #167 from larsbutler/cluster-controller-refactoring

ClusterController refactoring