CLI_COLOR support

[kcgthb]

Hi!

To build on #334 and #390, would it be possible to add support for NO_COLOR (https://no-color.org/) in ClusterShell?

[degremont]

I think CLI_COLOR would have more value there (https://bixense.com/clicolors/)

[kcgthb]

What about supporting both?

[dupgit]

Hi,
I propose PR #432 to solve this Issue. It implements both NO_COLOR and CLI_COLOR that has different purposes.
Regards,
Olivier.