add sleep after %firstboot to work around vmware bug

The sleep is a workaround for this:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=disp

The ticket states  that 30 seconds is a long enough  fix but we have
seen cases where it is not
Merge pull request #35 from gavin-scott/vmware-fix

add sleep after %firstboot to work around vmware bug