Template systemd/ceph-osd@.service with autotools,

Template systemd/ceph-osd@.service with autotools,

The libexec path is different for different distributions.
systemd. This path is defined by a new variable on the
configure path.

This variable can be set with enviroment SYSTEMD_LIBEXEC_DIR.
The parameter --with-systemd-libexec-dir overrides the enviroment
variable.

Appropriate conditionals are set for SUSE and RHEL derivatives.

This is then used to template out systemd/ceph-osd@.service

Signed-off-by: Owen Synge <osynge@suse.com>