Backed out changes that moved variables to p4_vars. The variables are intended to be in instance vars
to keep everything about a particular instance in one location. It was confusing for people to see
a setting in p4_vars and not understand that setting was being overridden in the instance vars.
There shouldn't be any overlap between p4_vars and instance vars anymore.
Also, server.id is not optional. It must exist. It is how you control whether the instance is a master
or a replica. It is not set by the scripts anymore because that was also confusing people. They would
try to change the role of a server by changing server.id and we previously would just overwrite their
changes. Now, the SDP just reads the server.id so that the user has control over it. That doesn't
confuse them since that is how our docs tells them to change a server's role.