MFC r296766:

Better handle filesystems mounted with -o noexec

ftruncate/11, open/20, and truncate/11 copy sleep(1) to a temporary file on the
target filesystem, execute the binary, then expect a result. This doesn't work
with scenarios where the target binary cannot be executed, e.g. the filesystem
was mounted with -o noexec.

Ensure the filesystem hasn't been mounted with -o noexec for the testcases
before executing them.