Deflake namespace e2e test by only asserting on jobs related to the
namespace tests. During our e2e tests, some left over jobs (e.g.
prometheus) are left running while being shutdown and cause the test to
fail.
Assert that deregistering a volume works without errors following a volume
reap. Use CLI helpers where feasible to exercise CSI command line. Dump plugin
allocation logs on deregistration failures for debugging purposes.
Exercises host volume and Docker volume functionality for the `exec` and `docker`
task driver, particularly around mounting locations within the container and
how this can be used with `template`.
The CLI helpers in the rescheduling test were intended for shared use, but
until some other tests were written we didn't want to waste time making them
generic. This changeset refactors them and adds some new helpers associated
with the node drain tests (under separate PR).
