Resolve the path in directory type chart sources relative to manifest

[zcrisler]

What would you like Loftsman to do?

Resolve the path in directory type chart sources relative to the manifest, not the current working directory.

Why is this needed?

To enable loftsman ship to be run from an arbitrary working directory without needing to edit manifest files.

This supports the current release process which downloads charts to a local directory packaged in a release distribution whose path relative to the manifest file is pre-determined. Although loftsman ship is generally orchestrated from an install or upgrade script, admins may also run it independently.