Revert "openstack-full, install-server: fix broken Debian builds introduced by"

This reverts commit df5b4021dcb10a6fd45be8e31a2b0f41f51674f4.
openstack-full,install-server: Install ruby-devel for Debian, refacto install_monitoring
Merge pull request #114 from enovance/refacto_install_monitoring

Refacto install monitoring