Fixes merge conflicts and standardizes option naming

the use of boto profiles for separating credentials as
specified in

http://boto.readthedocs.org/en/latest/boto_config_tut.html

This allows the EC2 inventory plugin to be used with
the same configuration against different EC2 accounts

Profile can be passed using --profile variable or using
EC2_PROFILE environment variable e.g.

```
EC2_PROFILE=prod ansible-playbook -i ec2.py playbook.yml
```

Added documentation on profiles to EC2 dynamic inventory doc

Only tries to use profiles if --profile argument is given
or EC2_PROFILE is set to maintain compatibility will boto < 2.24.

Works around a minor bug in boto where if you try and use
a security token with a profile it fails (boto/boto#2100)

Clarify why we add -q only for ssh

Python 3: the StringIO module is gone

Fixes 17 failing tests on Python 3.4, restoring the 8 failures we had
last Friday.

Output proper JSON from vbox dynamic inventory contrib script

fix no self pointer out of class.

Also get pipelining working for people who look to chroot as an example
for their own connection plugins

Note: In the latest v2 API, action handles become but chroot doesn't
reliably handle become.  Maybe we need to add a has_become attribute
that the action can display an appropriate error.

This can happen in chroot environments that don't have all of /proc
available

Helps connection plugin implementors understand how to structure
exec_command()

Fixes #12526

Update outdated comment

Since #12165 was merged, hostnames are properly validated.

We now use "sudo -n" instead of "sudo -k && sudo …"

Clarified that .yml, .yaml, and .json are allowable file extensions for inventory vars files

Also strip UnsafeProxy off of low level srings and objects to ensure
they don't cause issues later down the road

Fixes #12513

Typo in shell command in example