Create a common EC2 connection argument spec for EC2 modules

Refactor the currently well-factored ec2 modules (i.e. those that already use ec2_connect) to
have a common argument spec. The idea is that new modules can use this spec without duplication
of code, and that new functionality can be added to the ec2 connection code (e.g. security
token argument)
Merge pull request #5880 from willthames/ec2_modules_refactor

Create a common EC2 connection argument spec for EC2 modules