Only use ANSI terminal escapes if output is a TTY

[Jeremy Stanley]

Commands like 'git review -l' which colorize output should only do so when that output is destined for a terminal. If the output is a file or pipe, only plain text should be generated. Bonus points for a --no-color or similar command-line option, for people who aren't fond of it even when it is going to their terminal.

[Marcin Cieślak (saperski)]

Although I did some work on this, I'd be happy to remove color support completely from this feature.

[Jeremy Stanley (fungi)]

I'm not convinced it's worth the development effort to rip that out, but if someone comes up with a good way to limit it to actual interactive TTYs that would be welcomed (and a bit more correct, especially if done using the TERM envvar to determine whether ANSI color is even supported).

[Darragh Bailey (dbailey-k)]

Turns out I was already working on part of it, see https://review.openstack.org/#/c/106617

Would need to add the '--no-color' option to it.