CBQE-0: fix in raise Exception("some commands throw out error %s " %s command_with_error)

string format is not correct in
https://github.com/couchbase/testrunner/commit/8b09b364cb0fecdf2e265b31adbf397e93898456#diff-27305f4da838dfce5bb5a5dce214ee22R337

Change-Id: I10dc660248a9c7257069157e0f1bfaa572f5fc4a
Reviewed-on: http://review.couchbase.org/37038
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>