This change modifies how the the output from a CLI command is sent
to a client over AMI.

Output from the CLI command is now sent as a series of zero-or-more
Output: headers.

Additionally, commands that fail to execute (eg: no such command,
invalid syntax etc.) now cause an Error response instead of Success.

If the command executed successfully, but the manager unable to
provide the output the reason will be included in the Message:
header. Otherwise it will contain 'Command output follows'.

Depends on a new version of starpy (> 1.0.2) that supports the new
output format.

See pull-request https://github.com/asterisk/starpy/pull/34

ASTERISK-24730

Change-Id: I6718d95490f0a6b3f171c1a5cdad9207f9a44888