Speed up CI

[cgewecke]

PR:

• adds a missing statement to the circle logic that splits tests between parallel containers. (Both containers were running all the tests)
• upgrades ganache to V7 (~3X faster than V6)
• uses Node 12 container in CI (necessary for V7)

Cuts ~ 12 min (75%) from test job.

One consideration is whether upgrading the Node version here is ok. I think this is fine for set-ui since:

• we already install with --ignore-engines over there (by default it's pinned to 10.13)
• it's only for a dev dependency

Benchmarks	Branch	Test Time
master	17m 6s
PR	4m 53s