test if ssh keys work for kiln, github, before opening those services' pages

Summary: two things here: if your keys work already, then it just goes ahead and tells you things have succeeded. if your keys don't work, it goes through and walks you through how to populate them.

Test Plan:
user tested, went through process numerous times.

the first time, you see something like this: https://s3.amazonaws.com/uploads.hipchat.com/6574/27473/AdhFdmGiROVQd0g/Screen%20Shot%202014-05-14%20at%206.22.22%20PM.png

subsequent runs of make, you get something like this: https://s3.amazonaws.com/uploads.hipchat.com/6574/27473/yhFWRIUEPKSCgUk/Screen%20Shot%202014-05-14%20at%206.22.31%20PM.png

note that the script is only becomes interactive if some user intervention is needed

Reviewers: dylan

Reviewed By: dylan

Subscribers: desmond, chris

Differential Revision: http://phabricator.khanacademy.org/D8999