Bug 1412460 - Move configure invocation out of mach_commands.py; r=mshal

While we're here, also move the low-level code to invoke configure
to a proper Python module.

We needed to muck around with the log manager because the underlying
logger for output changed from "mach" (which is registered by default)
to something under the "mozbuild" hierarchy.

MozReview-Commit-ID: 4rlCxOwcVu1

--HG--
extra : rebase_source : e6c824a88fcfdbdeae31a7a94f33571f150e7690