(PDB-425) Move daemon-reload out of install-only

On upgrades, systemd service files may not have already been present, and they
might have changed. To address this, this commit moves the daemon-reload call
to systemctl out of the install only section of the %post, so that it is always
invoked. This will register the systemd service on upgrade from a sysv service
(as happens on fedora 18 through fedora 20) as well as register any changes to
the service file.
(PDB-425) Try SysV and SystemD on upgrades

On upgrades from PuppetDB < 1.6.0, even on platforms that support systemd, only
sysv will be in place. This means that when the status is queried in the %pre,
there won't be a systemd service file yet, so puppetdb will appear to not be
running even if it is. Next, when the service is stopped, also in the pre,
again there will be no systemd service to stop, even if there is a sysv service
running. This commit addresses that by testing for the existence of the systemd
service file, and if that is present, use the systemd service calls. Otherwise
it calls out to the sysv init system.
Merge pull request #833 from haus/ticket/1.6.x/pdb_425_fix_systemd_upgrades

SystemD upgrade improvements