skip broken versions

if we push a bad metadata version up to s3 we will not be able to parse
it and the exception that is thrown will break all downloads and will
cause an outage to omnitruck (if it occurred in production).  since this
is a terrible outcome, we just skip versions that don't parse.
add broken json to test.

this is effectively a functional test that we can still serve requests
even if we have one piece of metadata which is bad.
Merge pull request #71 from opscode/lcg/tolerate-busted-versions

Lcg/tolerate busted versions