[10.2.0] add support for puppet-systemd >= 7

[tuxmaster5000]

The last systemd module are not supported.

Warning: Module 'puppet-systemd' (v7.0.0) fails to meet some dependencies:
'puppetlabs-postgresql' (v10.2.0) requires 'puppet-systemd' (>= 4.0.1 < 7.0.0)