Enable and use salt_api proxy by default

 * Use nginx as proxy
 * Misc: define defaults for
    salt_master_host
    infra_config_address
    reclass_config_master
    jenkins_salt_api_url
 * Pass certs dir for jenkins docker slaves

Related: PROD-27641(PROD:27641)
Related: PROD-30528(PROD:30528)

Change-Id: I5fac90101131a8d8d4fa7857982f18c855e0771c
33 files changed