Foreman - generate apipie cache on postinstall

Generating cache for dynamic bindings. See https://github.com/theforeman/foreman/pull/1265 for details.

Scratchbuilds for testing:
- wheezy: http://ci.theforeman.org/view/Packaging/job/packaging_build_deb_coreproject/507/label=debian,os=wheezy/
- squeeze: http://ci.theforeman.org/view/Packaging/job/packaging_build_deb_coreproject/label=debian,os=squeeze/506/
- precise: http://ci.theforeman.org/view/Packaging/job/packaging_build_deb_coreproject/label=debian,os=precise/506/