This change implements the category / rule Server which will showcase
storig arbirtray alongside the hostname which are not part of hostname
generation.
This change moves the responsibility of calling the HostnameRule.Generate
function to the corresponding HostnameRule.{Insert,Update} functions
which will allow autonomy especially for the update functions on when
a hostname needs to be regenerated.
In BaseRule.baseUpdate our goal is to check if a hostname exists before
trying to rename that hostname into something else. This patch fixes an
error where the newly generated Hostname was used to check for the
existence of the old hostname.
Florian Beisel