the root e2e-tests.sh

[daisy-ycguo]

Currently, the root e2e-tests.sh does nothing except loop calling the e2e-test.sh under every single plugin. I think there are a few common set up steps that we might want to let the root e2e-tests.sh to handle:

• Set up Knative Serving and Eventing. We definitely don't want every plugin to set up and tear down Knative serving and eventing.
• Manage to call a plugin_setup() and plugin_teardown() for every plugins to set up their resources before the test and delete their resources after the test. ( This might not necessary. The plugin_setup() and plugin_teardown() could be easily put in somewhere of plugin e2e-test.sh).

@rhuss please share your thoughts to this two requirments.

[rhuss]

Totally agree, I just not have implemented it yet ;-) (although a "good" PR should only contain change to a single plugin and so only this plugin tests' are called for a specific PR, so only fire up a single cluster only, too).

Having test hooks sounds fine for me, but I think this can be already done by overriding some functions from the test-infra e2e-tests.sh script. But I will check.