Fix #1: Migrated to Alpine, implemented server_default cmd

[mrusme]

This PR contains two changes:

• Migrated the build stage as well as the final container to Alpine
• Implemented server_default as default CMD that is being executed through the entrypoint.sh by using the values defined in the ENV entries. Those values can be overridden using the --env argument of docker run. Also it allows for a nicer deployment on Kubernetes by using a ConfigMap resource for specifying those values.

This PR also fixes #1 by setting the default host to 0.0.0.0.

[fanzeyi]

Thanks, -crt-static is a neat trick. I'll merge this but I'm going to make some changes on the environment variable. structopt itself supports reading directly from environment variable like this so we don't really need to use entrypoint.sh for that.

lares/src/cli.rs

Lines 395 to 400 in af1527b

	#[structopt(
	short = "d",
	long = "database",
	env = "LARES_DATABASE",
	default_value = "lares.db"
	)]