cmd/frontend: add host as runtime argument
cmd/frontend: add host as runtime argument

This change allows for specifying a host address
at runtime. It is necessary to specify a host name
when running e2e tests within a docker container.

Change-Id: I3c41bd372e2ad71f798ca249929660191d2eead6
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/292698
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite