This is because we pass the whole dd command string into the shell
that's running on the contained environment rather than running it
directly from python via subprocess without a shell.
* 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.
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.
There doesn't appear to be anything that actually uses tmp_path in the
connection plugins so we don't need to pass that in to exec_command.
That change also means that we don't need to pass tmp_path around in
many places in the action plugins any more. there may be more cleanup
that can be done there as well (the action plugin's public run() method
takes tmp as a keyword arg but that may not be necessary).
As a sideeffect of this patch, some potential problems with chmod and
the patch, assemble, copy, and template modules has been fixed (those
modules called _remote_chmod() with the wrong order for their
parameters. Removing the tmp parameter fixed them.)
