This commit adds support for NO_COLOR environment variable, if this is
set, colors will be disabled in the logrus text formatter.
This commit also adds support for the environment variables supported by
logrus, CLICOLOR and CLICOLOR_FORCE
Related to #1549
Adds `STEP_LOGGER_ONLY_TRACE_HEALTH_ENDPOINT` environment variable to
opt-in to only logging successful /health requests at the Trace level
Fixes#420
Signed-off-by: Dominic Evans <dominic.evans@uk.ibm.com>