Handle packages which already have a 'build' directory
Use RPM macro for cmake

Using the %cmake macro adds some defines to cmake that allow for proper
debuginfo extraction
Allow threading on install stage of RPM builds
Add rosrpm to default build template

This will meake Bloom generate RPM specs based on the release platforms listed
in rosdep
Prevent missing RPM platforms from failing releases
Merge pull request #282 from cottsay/master

Finishing touches on RPM generation