Merge pull request #4979 from pbalcer/pmem2-ex-fix-no-ndctl

test: fix pmem2 example without libndctl

src/test/ex_libpmem2/out5.log.match

 $(OPT)pmem2_source_device_usc: Unsafe shutdown count is not supported for this source
 $(OPT)pmem2_source_device_usc: Getting unsafe shutdown count is not supported on this system
+$(OPT)pmem2_source_device_usc: Cannot read device usc - ndctl is not available
 foobar