support configuring bridge interfaces on EL-based distros

I'm not too familiar with Debian/Ubuntu-based distros, so didn't implement this for the Debian ::osfamily case.

Under EL, you can specify the parent bridge device in the child device's config.  But under Debian/Ubuntu, you have to specify the child devices in the config for the parent, I think.  Not sure the best way to handle that.

Happy to implement it, though, if someone else can help come up with a sane way to do it.
Ah, yes, you're right.  Our OVS packages were custom builds, so they have different names.  I'll submit a new PR with configurable package names.