hack/e2e-test: Set the executable bit

This script has been 100644 since it landed in 8bcee7e (Add e2e test
that installs hive and creates a cluster, 2019-01-25, #191).  I'm not
sure why that wasn't a problem before, but I just saw [1]:

  hack/e2e-test.sh
  make: execvp: hack/e2e-test.sh: Permission denied
  make: *** [test-e2e] Error 127

[1]: https://storage.googleapis.com/origin-ci-test/pr-logs/pull/openshift_hive/222/pull-ci-openshift-hive-master-e2e/106/build-log.txt

Author: wking