ssh connection plugin: Make comments more verbose

Explain _communicate() more.
Bugfix, fix crontab commands on HP-UX
If memory not available in syslog.log, catch error, attempt to find it with adb
Output URL for debugging
Make `vpc_security_group` docs more accurate

Without the `subnet` parameter supplied there's an error `msg: Parameter vpc_security_groups invalid for create command`. (This might be a bug?)

If the VPC security group name rather than ID is supplied there's an error: `msg: Invalid security group , groupId= <some group name>, groupName=.` (Accepting a group name might be a feature enhancement.)

In my case I set the subnet as `default` and used `register` to get the result of the security group creation section and just referred to its `group_id` property.
Check for errors from adb, may not work on all systems.
module_retention isn't defined anywhere, including the help.
Remove extra quote from the mysqldump password argument

The mysqldb Ansible module will fail if the state specified is import or dump with a '1045: Access Denied' mysql error for complex passwords.

This is caused by the extra quote around the '--password' argument to mysqldump, as pipes.quotes already quotes the password string.

>>> "--password='%s'" % pipes.quote('simple')
"--password='simple'"

>>> "--password='%s'" % pipes.quote('c0mplexp@ssword!')
"--password=''c0mplexp@ssword!''"

>>> "--password='%s'" % pipes.quote('password with space')
"--password=''password with space''"
Clarify the port value always defaults to 3306

While the [boto docs](https://github.com/boto/boto/blob/develop/boto/rds/__init__.py#L253) make it seem like the default value of `port` is changed depending on the engine chosen, AFAICT from looking at the code the default value is never changed from 3306.

I think the docs are intended to be read as "the default value used by <engine> is <port> so you should change `port` to that value".

If you don't specify the port value and chose the database engine as PostgreSQL you'll end up with a PostgreSQL instance running on port 3306.
Merge pull request #6795 from jjshoe/patch-2

module_retention isn't defined anywhere, including the help.
redhat_subscription calls AnsibleModule() without argument_spec

The Rhsm object requires an AnsibleModule but it isn't created with an argument_spec and fails.  Since the rhn.module is set directly after, setting None for the required argument of Rhsm fixes the module.
Use /usr/bin/python instead of /usr/bin/env python
Merge pull request #6805 from sivel/env-interpreter-fix

Fix interpreter lines in a couple of modules
debconf detail requirements and fix typos
Fixes to safe_eval
Splitting SETUP_CACHE into two caches, one for host vars and one for setup facts
Adding wait/wait_timeout parameters to the ec2_key module

Fixes #6455
Updating CHANGELOG for ec2_key wait addition
Fixed cwd for submodules update
Catch permissions errors related to opening a known_hosts file

Catch permissions errors related to opening a known_hosts file