Create package repos even on failure

Created by: olafurpg

Many reasons can cause Sourcegraph to fail to create a package repo. For example:

• Invalid resolution configuration like missing Artifactory credentials
• Missing sources.jar, some dependencies have no sources

Currently, we log error messages and/or panic in these cases. However, there's not much Sourcegraph can do in these cases except report the error to the user. In many cases, these errors are normal and there is nothing to do.

It would be nice if we went ahead and always created package repos, even on failure. In case of failure, we can create a readme.md file explaining the failure (including error messages or stack traces).