feat: make lazy stream host name configurable

[taylorbourne]

so this is going to be a breaking change (which is funny since things are already broken) but everyone will need to set the new variable...

Makes more sense this way anyway. I have a pretty solid fork of Xteve going so maybe we can bake some of this stuff in in the future. For now, this'll do.

[tarkah]

Sorry, I was out on vacation for a few days. I'm not sure this is a good change for our end users.

I think lazystream should be responsible over defining an "override" to the default host. See tarkah/lazystream#86.

My thought is I'll also add a subcommand for lazystream called host which just outputs the configured host name. Then lazyStreamHost can be changed to hostOverride. We can then do something like the following pseudo-code:

override = if $hostOverride; then "-host-override $hostOverride"; else "";
export IP=$(getent ahostsv4 $(lazystream $override host) | awk '{ print $1 }' | head -1)

And same when calling lazystream in the cron script.