"repozo --verify" is not working as this code expects it to: it simply
prints errors in stdout, and doesn't return an error code in case of
error. Thus, running it had absolutely no effect, except wasting IO
and CPU time.

This commit introduces the use of "repozo --recover --with-verify",
which runs the verify and the recover in a same step, and has the
advantage to raise (it doesn't exit with 0) in case of error. Also, as
it does the verification and the recovery at the same time, it uses
half the IO for the read. On a production server using SSDs, with a
ZODB of 1Tb, runner-import-restore now takes 14h instead of 26h, iow a
performance increase of 46%.