scripts: tweak runner-related command output

Having common log handlers now lets us improve our logging output so
that info messages are prefixed with the runner they came from, and
doing something similar with the high level steps as we go, like this:

   -- west <command>: using runners
   -- runners.RUNNER_NAME: doing something
   <output from RUNNER_NAME subprocesses go here>
   -- runners.RUNNER_NAME: all done, bye

We can also colorize the west output to make it stand out better from
subprocesses, using the same output formatting style that west
commands like west list do.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>