Added ability to suppress invalid key warnings on non-openbsd systems

This lets you use the sysctl module to manage keys such as:

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0

Which it currently fails on because sysctl requires the -e (suppress errors) is used to put those keys into the sysctl file.

hiera looks like:
sysctl::value:
    net.bridge.bridge-nf-call-arptables:
        value: '0'
        suppress: true

For these values.