foreach mode for --failed or --succeeded

[rnorth]

During #141 @Dan7-7-7 suggested having a flag so that turbolift foreach could be run just targeting repos that failed on the previous run. Combining a couple of ideas, I think it could be possible if foreach's file-based output uses timestamped temp directories, which would enable to tool to figure out which repos failed or succeeded on the preceding run.

[sledigabel]

We could retrieve the last one by creating a symlink called last during the preceeding foreach and point it to the tmpdir.

[sledigabel]

this last symlink would be at the root of the campaign.