CBQE-0: don't run tests if installation failed

it's additional verification if CB installed succesfully:
does not require changes in the jobs

Change-Id: I3f8b5fd7c5a512434eb61b940483dfb5e5df02cf
output: https://friendpaste.com/3fk7mgOiStKrV27vzNs8zT
Reviewed-on: http://review.couchbase.org/37435
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>