Only allocate a PTY when sudo is used

Postpone the paramiko.Channel.get_pty until we know sudo is used. If
sudo is not used, then we do not need a PTY. In fact, the paramiko docs
explicitly state that it's not desirable to allocate a PTY for a simple
exec_command.

Signed-off-by: martin f. krafft <madduck@madduck.net>
Initialise PTY from calling environment

If we need to acquire a PTY for sudo's use, then it should really
inherit the capabilities of the calling environment. This is what
OpenSSH does, and so it makes sense to copy this behaviour for the
paramiko connection type.

Closes: #2065
Signed-off-by: martin f. krafft <madduck@madduck.net>
Merge branch 'paramiko-termcap' of git://github.com/madduck/ansible into testing