CBQE-1013: Triage/Fix failures for ubuntu upgrade job

restore data/index_path after offline_cluster_upgrade_non_default_path.
now values for self.input.servers are not re-read after each test in testrunner

for example, if we changed server values during the test then the same values will be used in next tests

Change-Id: I0a32dcdce279f7db1bf646f86f70fbb368288dc6
Reviewed-on: http://review.couchbase.org/24386
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>