[e2e] Add option to use existing clusters, this can reduce the time to run tests as cluster build and tear down are not needed for each test run

Currently the e2e tests create a new cluster each time called the `etcd-test-cluster`. This is a kind cluster and it takes time to get created. We ideally also want to allow the option to use the existing cluster where all the test components for etcd can be deployed.

ref: https://github.com/etcd-io/etcd-operator/issues/159

cc @ahrtr @ivanvc @ArkaSaha30 @jberkus @hakman