update preemption tests to use new node resource structs

also includes a fix to remove unnecessary subtraction of network mbits

Preemption for system jobs

Fixing mistake in reschedule doc

Register exec driver plugin among some fixes

Also added test case

Fix driver naming, fingerprint output, races/tests

UI: build time performance improvements

also removed now unused method

UI: Reset page query param on search

Update changelog with GH-4819

Namely, remove the `enabled` configuration flag, as it's specific to
`raw_exec` driver.  Also, pass resource limits to underlying call.

Allow artifacts checksum interpolation

In tests:
* always cleanup (Kill) the harness
* don't call SetConfig more than once (a race)
* avoid cgroups to allow running without being root