[Bug 991099] Upgrade to ElasticUtils 0.9.1

I based this off of mozilla/fjord#254, where @willkg did the same upgrade. My strategy was to do the library upgrades, and then bash the code until the tests passed. When testing, make sure to update git submodules.

I rebased this against master, so @r1cky's recent MLT changes shouldn't break anything.

r?