this is mostly just a workaround for 669034. Seems like
plexus-container-default has some quirks that cause it to lose
version so it's set to null. Needs more looking into to fix it
properly.
- Install maven metadata so they are not downloaded when mvn is run (667625)
repo-metadata.tar.xz will have to be updated as additional plugins need new metadata
- Make sure JavadirWorkspaceReader is used when building model (patch update)
Needed because WorkspaceReader is not used early when building mvn project
and this causes problems
- JavadirWorkspaceReader doesn't pretend to resolve non-existent artifacts anymore
Instead it returns null (artifact not found) so that reactor/local resolver can work as expected
