GitLab

- set env variable for GNI provider to work alongside MPI
- add bandwidth tests

(need to make similar updates for static build version)

suggested by Howard Pritchard to avoid potential conflicts with mpich

current master version of mercury should automatically enable SSE4
checksumming, which is not expected to impact performance

- switch back to mercury origin/master (has bmi updates merged)
- switch to branch of argobots with mutex wakeup fix

- disabled for now; example hangs on Theta

- untested

This reverts commit 7eb816a2.
- necessary fix has been upstreamed

- have not tested benchmark execution yet, just setup, build, and submission