Allow /configuration calls to accept apiRoots different than production bzapi's.

[KWierso]

Right now in 0.4.3, calls to /configuration are hardcoded to the production bzapi. It'd be nice if this could accept a different api root, if provided (so we can test against https://bugzilla-dev.allizom.org/bzapi/configuration for instance).

I'd also suggest switching the production /configuration call to use https://bugzilla.mozilla.org/bzapi/configuration instead of https://api-dev.bugzilla.mozilla.org/latest/configuration but that's neither here nor there...