Do not hardcode rpmbuild location - could cause problems during OS init phase

I've updated build.sh and default recipe for rehl since I spent a lot of time figuring out why runit wouldn't install during OS init process bootstrap. 

Turned out that /usr/bin/rpmdev-setuptree which is used inside build.sh uses rpm --eval to get and create rpmbuild folder locations.

If you run the chef-client process as part of OS startup ( for example if you use amazon EC2 ) your RPMS folder location will be determined by running rpm --eval "%{_rpmdir}" --> /usr/src/rpm/RPMS which is not /root/rpmbuild folder as hardcoded in cookbook.

That will cause all sort of build and rpm install problems.. I removed those hardcoded parts from the cookbook and hope it will save someone copule hours (days) of debugging.