Show exception details for failed deploys.

Without some detail errors are inscrutable and impossible to debug.

Fixes bug 1178608

Change-Id: I0ed6164e8689c63bd194924d3f7cb50b49feb921
Allow different paths for deploy-helper helpers.

Different distros (or even distro releases) put iscsiadm in potentially
arbitrary paths. It is better to use rootwraps' own search than to hardcode the
path.

Fixes bug 1178612

Change-Id: I690788b666a84e599504690d0e2d087eaa66a4c8
Merge "Show exception details for failed deploys."
Merge "Allow different paths for deploy-helper helpers."