Option to specify profile

[railadeividas]

Allow having few profiles in default config .s3cfg

[deividasraila]

@fviard please check

[fviard]

Thank you very much for your PR that is quite good and would solve an issue that is encountered by quite a few users and sorry for the long delay for my feedback.

If it would still be possible for you, there is a little change of behavior for this feature that I would prefer:

• Currently, for the s3cfg file, it will read one section or another (so either the default or the profile one).
• I think that it would be better to always try to load the "default" section, and to then optionally load the "profile" on top of that.
• It would probably be easy to do a first version with a slight modification of your code.
  Something like creating the ConfigParser with the "[default]" sections, and then if there is the profile, use the "parse_file(...)" function of this cp instance with the "profile" as [sections].

I think that it would be better because if you have to copy paste all the common options in all your profiles, there is not that much any interest compared to use multiple config files. But with this, you could have a common (default) config and just put the specific parts inside each profile.

I added 2 nitpicks directly in review comments.

[deividasraila]

@fviard I have updated and tested the code to always load default.