ts-depriv-audit-qemu: Leaked substeps are `blocked', and then script is fail

ts-depriv-audit-qemu: Leaked substeps are `blocked', and then script is fail

If thus script crash in some non-substep-specific operation, the
substeps may have been created (and thus be in the db as `running').
Leaving them like this is not allowed: it is treated by sg-run-job,
and by the archaeologists as an internal error.

If this happens, what we want is for the script as a whole to be
`fail', and for the failing tests to be `blocked'.  The former will
spot if this crash is a regression.  The latter will avoid treating
the substeps themselves as regressions.

Reported-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>