removing colours from loggo package

[roger peppe]

In August, the loggo package was changed to make it log ANSI-terminal
colour escape sequences by default.

I'm not sure that was the right decision, for a couple of reasons:

- daemons are often given a pseudo tty to run in, so the log files
produced by our running services are now obscured by escape sequences,
making them hard to process automatically (and larger).

- it means that the loggo dependencies are much larger.  Where
previously the loggo package had no non-stdlib dependencies, it now
depends on 5 significantly sized repositories holding >100k lines of
source, including at least one system-dependent (Windows-only) repo.

I'd like to propose that we remove the colour-by-default logic from
loggo and move it to a separate package where it can be used if
required by a given client. Perhaps github.com/utils/loggocolor might
be a reasonable place.

Then we can change the juju command line client to use that writer by
default meaning there should be no change in externally visible
behaviour to juju client users. The jujud server executable should
probably not be using coloured logging output IMO.

Thoughts?

  cheers,
    rog.