CB-6307 minor bugs

- re-execing with the modified ulimit would hide all the output and mask
  non-zero rc when there was an error. It should show the output and let the
  non-zero rc cascade out.
- the "--sign" argv for create-archive was not properly typed to boolean. So
  doing "--sign false" did not have the intended result.
- if not signing the archive, it still failed if 'gpg' was not present.
- when unzipping the zip archive of the source, there is no leading prefix.
  Thus when unzipping multiple repo archives, they will step on each other
  unless you first manually create separate subdirectories for each repo zip.
  Although this isn't technically an error, I think it would more friendly if
  the zips were already separated into different subdirectories when you unzip
  them.