add support for availability zones

[coyotemarin]

We should add an availability_zone option to EMRJobRunner that lets you run job flows in specific availability zones (essentially, data centers).

[irskep]

Should be done in my az_support branch (https://github.com/irskep/mrjob/tree/az_support) but I have not been able to fully test that it works. I can, however, confirm that it doesn't break anything.

Boto and Amazon appear to have a slightly different API for job descriptions. Amazon nests instance information (master/slave type, number, AZs, etc) in an InstanceConfig object called Instances, while Boto flattens it all out. I couldn't convince myself entirely that Boto actually works one way or the other, so I'm still testing that one by hand.

Edit: Job descriptions will most of the time have the 'availabilityzone' instance variable. Most of the time.

[irskep]

All day I have been asking myself the question, "Why is aws_availability_zone being ignored by no one except EMR?" The answer, it turns out, is that there is a bug in boto that sets the wrong key for the availability zone in the job flow configuration. So I will be sending them a pull request as well. The MRJob copy is fixed in my branch.

[coyotemarin]

Fixed in development-v0.2.x.