Support RBAC

[tgross]

For https://github.com/joyent/python-manta/issues/25, in support of https://github.com/tgross/triton-mysql/tree/working

Update the client to support roles and subusers:

• The MantaClient constructor now takes optional subuser and role parameters and adds these values to the Authorization and Role headers, respectively.
• The mantash CLI gets the params from either the --user / --role command line arguments or from the MANTA_SUBUSER / MANTA_ROLE environment vars. This behavior matches the Node.js Manta client.
• README is updated with instructions for setting up a Manta subuser for tests.

@trentm this is probably ready for review but not a merge yet -- there's one test that I can't get to pass with a subuser, which is the snaplink test. But I've discovered I can't get that test to work with the node client either. I'm investigating that now.

cc @misterbisson

[tgross]

I've opened https://devhub.joyent.com/jira/browse/MANTA-2829 for the snaplink problem. I'm pretty sure it's not just a misconfiguration of the role at my end, but hopefully someone who knows things better can confirm that with all the info I dumped there.

[trentm]

Otherwise, this all looks great to me.

[trentm]

@tgross let me know when you have updates for the above, then I think we could integrate this. Perhaps we couldhave the test case skip the snaplink thing if using a subuser for the test run (emitting a warning pointing to the MANTA ticket).

[tgross]

@trentm updated.

[trentm]

I hadn't realized that about Python 2.6. I still have a module that supports Python 2.4. :) But yah, it was just the one spot. print "Old string interp %s" % "forever!"

[trentm]

Added changelog entry, bumped ver to 2.5.0, squashed and merged in commit 3ada868.

[trentm]

published to pypi as version 2.5.0.