tmpfiles: add a new return code for "operational failure" when processing

tmpfiles: add a new return code for "operational failure" when processing

Things can fail, and we have no control over it:
- file system issues (immutable bits, file system errors, MAC refusals, etc)
- kernel refusing certain arguments when writing to /proc/sys or /sys
Let's add a new code for the case where we parsed configuration but failed
to execute it because of external errors.