* Disable su as it's not currently working 100% (and was disabled in v1).
* Move BUFSIZE out of the class to match other conenction plugins
* _connect shouldn't return self.

requested via play context

cloudstack: improvements and tests

#9130 rebase: EC2 Inventory Boto Profile Support

Re-order the methods in ssh.py so that methods needed for implementation are near and just above the relevant public methods.

Standard with the rest of the code base.

A couple of ssh cleanups

Make use of better error handling mechanism

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)

Make pipelining a connection variable

This is also peripheral to what _build_command needs, can be improved
and tested independently, and so makes more sense in a separate method.

This commit doesn't change any functionality (and I've verified that it
works with the various combinations: control_path set in ansible.cfg,
ssh_args adding or not adding ControlMaster/ControlPersist, etc.).

Checking for sshpass is peripheral to the calling code, so it's easier
to follow when the details are moved into a method.

SSH pipelining can be a significant performance improvement, but it will
not work if sudoers is configured to requiretty. With this change, one
could have pipelining enabled in ansible.cfg, but use sudo to turn off
requiretty in a separate play (or task) where pipelining is disabled:

    - hosts: foo
      vars:
          ansible_pipelining: no
      tasks:
        - lineinfile: dest=/etc/sudoers line='Defaults requiretty' state=absent
          sudo_user: root

(Note that sudoers has a complicated syntax, so the above lineinfile
invocation may be too simplistic for production use; but the point is
that a separate play can do something to disable requiretty.)

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

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