test/rocksdb: move nightly test case to RUN_NIGHTLY_FAILING.

rocksdb has been frequently failing in nightly tests:
https://ci.spdk.io/spdk/nightly_status.html



Change-Id: I53d812dfb6146bd973fff3c40fe3490c0fba9fc8
Signed-off-by: Pawel Niedzwiecki <pawelx.niedzwiecki@intel.com>
Reviewed-on: https://review.gerrithub.io/406975


Reviewed-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>