tests: verify that UTIME_OMIT works
tests: verify that UTIME_OMIT works

It currently does not and even causes a crash due to a bug in
go-fuse.

Also converts the test to table-based.

davesteele/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs,rfjakob/gocryptfs,davesteele/gocryptfs