fix extra_groups and add create user options

If you want create a group with the same name as the user do it now simple.
Use:

   fabtools.user.create('alice', group='alice')



fix extra_groups bug for madify
relocate crypto import

this fix need if you have not crypt package.
Merge pull request #61 from pahaz/master

Add create user options - create_group_if_need=True