Fix issue where startup of salt-master leaks memory

On salt-master startup I stared seeing "WARNING: Mixing fork() and threads detected; memory leaked." in stdout. After doing a git bisect I found that c2e96e had been the commit to cause the issue.

c2e96e moved the init of various classes around. While doing so all of the module class init was moved into the parent process (pre-fork), which means that if any modules create threads we will leak memory (at least)