viewmerge tests don't work on single node

When running the viewmerge tests on a single node they fail.

To reproduce:

• run single node cluster
• start testrunner with:
  ./testrunner -i b/resources/dev-single-node.ini -c conf/view-conf/py-viewmerge.conf

If you comment those 3 lines out [1], the test passes.

[1]: https://github.com/couchbase/testrunner/blob/d8c6ac4cc6448d0488c050667f56ef31c3838e33/lib/membase/api/rest_client.py#L197-L199