tools/veyron/impl: allow repositories to have a different name and a path
tools/veyron/impl: allow repositories to have a different name and a path

Before this change, the veyron tool assumed that all repositories are
located at a path that matches their name. This CL lifts this
assumption by parsing the manifest.xml (as opposed to project.list).

Change-Id: If5f23201d82771b93f110e3bd371b3bad5eefadc

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools