*.hhvm.beta.wmflabs.org -> *.wikipedia.beta-hhvm.wmflabs.org

Having en.wikipedia and en.hhvm is confusing, because it uses the same slot
within the hostname to mean two different things: in one case, the project; in
the other, the interpreter. To fix this, I moved the interpreter to the
first-level subdomain.

Change-Id: Idc4bea0ea4bf2620ae6a9e8a11d1e7d69229da89