authentication: allow to set tuxapi/tuxauth url env variable

when running tuxtrigger lambda on dev environment, we don't have mechanism to set and use config file( wherein we can manually define group/project and tuxapi/tuxauth enpoints to use ) for tuxsuite authentication which limits our current use case. As we only rely on TUXSUITE_TOKEN to use tuxsuite in lambda, which will work fine for prod env ( as group/project can be identified from token itself ) but this is currently not possible for dev environmets as dev endpoints are needed to do the same. This patch will allow us to manually set and use dev tuxapi and tuxauth url to be used to get group/project from dev token itself.

Signed-off-by: Alok Ranjan alok.ranjan@linaro.org