These changes introduce dual Mongo support into the Meteor
Tool. 32-bit Mongo (3.2.15) will be used by Meteor when the
Tool is run on a 32-bit OS (32-bit Linux and Windows). 64-bit
Mongo (3.4.9) will be used when the Tool is run on a 64-bit
OS (64-bit Linux, Windows and macOS).
Fixes https://github.com/meteor/meteor-feature-requests/issues/129.
For some reason I decided that tests should, on cleanup, stop their
runs *and not wait for the stop to take effect* before running the next
test. Maybe this could be reconsidered but for now, explicitly stop this
run (and wait) so the next test (npm: npm) doesn't fail.