Jobs run as non-privileged user

nats should run as vcap user
cf_registrar should run as vcap user
uaa should run as vcap user
login should run as vcap user
nats_stream_forwarder runs as vcap user
collector should run as vcap user
local syslog aggregators should drop root permissions

[#73622734]

Signed-off-by: Julian Friedman <julz.friedman@uk.ibm.com>