rabbitmq needs HOME env to be set, always set runas to set that var.

Set default user for running rabbitmq cmds to user that salt-minion runs
as. Fix #17226
Revert "default run as root user because ``erlexec`` needs HOME env to be set"

This reverts commit ce91c65a7766fe784f9f87a9be59e47d7551e813.

Already set user to run rabbitmq cmds in rabbitmq module to whom
salt-minion running as.
This allow to specify arbitrary user to run those cmds
but still has a saner default than 'root'.
Setting it as 'root' may not work when salt-minion does not run as 'root'.
add runas parameter for all functions
pep8