Fixes #8 Set selinux context of cache_dir and ports.

[ralfbosz]

When SELINUX is enabled the cache_dir and port are given
the correct SELINUX context (fcontext & port)
Only works on RedHat and families

[ralfbosz]

Works only on osfamily == "RedHat".
Didn't include the requirement in metadata.json, since the selinux module isn't supported on Debian and more.

[ekohl]

Usually it's good to mention soft dependencies in the README.

[traylenator]

@ralfbosz , thanks. Have been meening to do for a long long time.
I'd say this is a good case for an acceptence test. However happy to merge as is also.

[ralfbosz]

Figured out one issue (and confirmed it with a quick test), the fcontext for the cache_dir is set, but not applied (with restorecon). Need to think of a way to trigger that...

[ekohl]

@traylenator I recall that SELinux is disabled inside the docker containers we use to test on Travis. It'd be good to know it's not breaking on SELinux disabled, but it wouldn't verify your intended functionality.

[traylenator]

@ekohl Okay - agreed without selinux enabled it is next to pointless.