PEP8-ification of the sources.

	modified:   cluster.py
	modified:   conf.py
	modified:   exceptions.py
	modified:   helpers.py
	modified:   main.py
	modified:   providers/__init__.py
	modified:   providers/cloud_providers.py
	modified:   providers/setup_providers.py
	modified:   subcommands.py
Fix typo and allow -v option to be given to all the subcommands
Minor improvements on the UI
Add `pre_run` method to main program and subcommands, in order to check the values of the supplied command line options.
Merge branch 'master' of github.com:gc3-uzh-ch/elasticluster