(maint) Update rpm spec and systemd service file for pidfile handling

Previously, the rpm package was creating /var/run/puppetdb at install time for
pidfile storage. This will break on modern Fedora/RHEL and SUSE systems as
/var run (which is a symlink to /run) uses tmpfs and will not persist through a
reboot.

This updates the RPM spec and systemd service file to properly handle creation
and removal on /var/run/puppetdb on systems using tmpfs.
(maint) Update "sles-release" dependency to "distribution-release" virtual package

The "sles-release" package only exists SLES. distribution-release
is a virtual package that will install sles-release on SLES, or
OpenSUSE-release on OpenSUSE.