remove knb_test from regular test suite, run only on special request.
by using a name for the test file not starting with test, test_that::test_dir() will ignore this test.
It can be run with test_file(knb_test.R) instead.  The test relies on the dev server instance, which
is not always up and running, so may fail without any fault in the codebase.  The test also requires
authentication for write permissions to knb, and so may fail if an unexpired CIlogon certificate is
not available.  Therefore, the test should only be run explicitly after verifying that the CIlogon
certificate is up-to-date and the dev server is responding appropriately.

Note that the REST-based dataone client may lead to changes in this function later.