Bug 1434943 - Update MozillaBuild version to 3.2 for NSS

[martinthomson]

We need to run 3.2 if we're going to use the vswhere tool to find VS. That won't change the calculus for these builds, but it's a big usability improvement for contributors.

[martinthomson]

Oh, I should point out that this shouldn't be merged until we have merged https://phabricator.services.mozilla.com/D5483 on the NSS side. Otherwise we won't be able to find nsinstall - the reason we stayed with 3.1.1 in the first place.

[coveralls]

Coverage decreased (-54.7%) to 15.468% when pulling a42b71e on martinthomson:update-mozilla-build into 68db461 on taskcluster:master.

[petemoore]

Apologies Martin! I should have asked you to update nss-win2012r2-new instead of nss-win2012r2.

I'll leave this PR open for now, since if all goes well in staging, this PR can roll it out to production, and I'll push the same changes to staging now...

[petemoore]

@martinthomson I've applied these changes to staging in 654bc76 and am currently running the deploy script to roll it out to production.

In an hour or less the images should be rebuilt and propagated to production, then this patch can be used to run try jobs using Mozilla Build 3.2.