console: Env vars for coverage args
console: Env vars for coverage args

Encourage use of environment variables for coverage command line
arguments, GJS_COVERAGE_PREFIXES instead of --coverage-prefix, and
GJS_COVERAGE_OUTPUT instead of --coverage-output.

This is because we want to pass arguments occurring after the script on
the command line as arguments to the script and not to GJS. Without
environment variables, it would otherwise be impossible to turn on
coverage, for example, for a script that started with #!/usr/bin/gjs.

https://bugzilla.gnome.org/show_bug.cgi?id=772033

endlessm/gjs,endlessm/gjs,endlessm/gjs,endlessm/gjs,endlessm/gjs