test/docker/run: Stop caching artifacts

Trying to cache artifacts like this causes surprises where a different
version of plugin or gerrit is being tested than expected.

We don't expect a --gerrit-war often during normal plugin development,
but add a default of bazel-bin/events.jar for the plugin jar option
so that it doesn't have to be specified to run tests.

Using the 'bazel test docker-tests' command is still better because it
ensures the plugin version you're testing matches the tree you have
checked out.

Change-Id: I126c891c47c5919e9cb58c5b3bbb99414e827c6c
3 files changed