cmake: add the autoconf path variables back

cmake: add the autoconf path variables back

* partially revert 7a602ec.
* the directory variables created by automake, like "prefix", "bindir",
  and "libdir", are used for generating configuration_file() for substitution,
  and they should have the same names with ones from autotools.
* also fix the ${pkglibdir}, it should be the ${libdir}/${PACKAGE}. so
  the plugins are not installed into ${libdir}, in which the installed shared
  objects are supposed to be shared with other applications.
* install shared libraries into ${CMAKE_INSTALL_LIBDIR} instead of
  ${prefix}/lib. this complies to what ceph.spec.in requires:
  ceph.spec.in expects the shared libraries to be installed into
  ${_libdir}, and ${_libdir} is /usr/lib64 on an amd64 machine.

Signed-off-by: Kefu Chai <kchai@redhat.com>