Ceph

When Ceph was installed on a pre-`/usr merge` [1] distribution that is upgraded to Quincy, the osd_class_dir seems to be incorrect. This may be due to a change in behavior from cmake where CMAKE_INSTALL_DIR changes to a relative path. Cmake's documentation says that CMAKE_INSTALL_DIR can be an absolute path but should be relative [2].

Gentoo has already applied this patch [3] to resolve the issue and Ubuntu is working on the same.

1: https://lwn.net/Articles/890219/
2: https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html
3: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=5ae443701f3ac7d74af946097041380e9a8e2014