twister: Add option to always force color output

Colorama, by default, strips out the color escape characters when the
output is redirected, and this may have an unintended consequence of
disabling color outputs when using a utility such as `tee` and in the
CI runners that redirect the stdout and stderr console outputs.

This commit adds a new command line option called `--force-color` to
always force the ANSI color escape sequence output even when the output
is redirected.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>