Support for profiles with assumeRole and MFA by using boto3

[takeda]

I submitted a PR: #1 which allows to use profiles with assumeRole and MFA, features which are not supported by the old boto.

This also helps with effort to move to boto3 and is needed for migrating the code to work in Python 3. Boto does not work on python 3 and is no longer maintained.

[takeda]

@AmineChikhaoui any opinion about my PR? Can it be merged? I can continue the work and ultimately make the code work on Python 3, but I need to know that my work is not waste of time. This is the second time I am submitting this PR (was unlucky to do it at the same time there was work in progress to split nixops into smaller pieces)

[AmineChikhaoui]

Hi @takeda , I haven't looked at the PR yet. I'll try to do that next week.
And thanks for re-working the PR after the split :)

[dnaq]

Just wanted to check in to see if this is planned to be merged at some point or not.