Moved AWS modules over to common module fragments

Created common module doc fragment, and applied to all
modules that use ec2_connect or connect_to_aws as
they definitely share the common doc fragments
Use common code for ec2_elb and ec2_elb_lb

Uses the new get_aws_connection_info
and connect_to_aws common methods to reuse code

Now complains if region is not set in one of the
three possible methods

Also moved over to common documentation code so
this is actually based on #6913
simple random filter
Refactor play._update_vars_files_for_host to make common functions and easier debugging

Fixes #4883
Add unit tests for vars_files
Merge pull request #6913 from willthames/aws_module_doc_fragments

Use common module document fragments for AWS modules
Merge pull request #6914 from willthames/elb_redo

Use common code for ec2_elb and ec2_elb_lb
Merge pull request #6917 from bcoca/random_filter_clean

simple random filter
Fixes #6929 remote file module doc fragments from copy and template