Only run Makefile during build phase (not install)

Currently, `Makefile` is re-run when catkin installs the package. This causes `Makefile` to re-install, this time leaving the files in `/` instead of an intermediate directory. This ensures that once built, `Makefile` is not re-run.
Merge pull request #375 from cottsay/master

Only run Makefile during build phase (not install)