Work around false positive in checkbashisms

 - Nothing wrong with the plugin, but checkbashisms triggers on the
   presence of a variable called $HOSTNAME

 - Changing the variable name in the plugin is the "easy way out".
Remove unimplemented but advertised "autoconf"
Update documentation
Check if we are running as a user required by rabbitmqctl
Fix mis-spelled variable names
Handle missing rabbitmqctl