Two issues with the env-aware NoColor() introduced together with
HELMFILE_NO_COLOR / NO_COLOR support:
1. Color() consulted the raw GlobalOptions.NoColor field instead of
NoColor(), so in a TTY with only the env set, Color() fell through
to terminal autodetect and ValidateConfig() spuriously errored with
"--color and --no-color cannot be specified at the same time".
2. NoColor() returned true via env even when --color was explicitly
passed, so `helmfile --color` with NO_COLOR (or HELMFILE_NO_COLOR=true)
in the environment hit the same ValidateConfig() error. A flag should
always win over an env var.
Fix both by routing Color() through NoColor() and giving NoColor() an
explicit --color short-circuit. Regression tests added for both paths.
Signed-off-by: Dominik Schmidt <dev@dominik-schmidt.de>
ef8ed9e6bc