Tools attribute improvements for RecyclerView LayoutManager.

1. Change tools attribute for layout manager from layoutManagerType to
LayoutManager.
2. Support classnames in the tools attribute.

This change doesn't try to supprt arbitrary classnames for now. The
reason for this is that the new layoutlib API is supposed to contain a
new method for inflating custom classes that are not views. This will
allow us to throw better error messages. Without the new API, trying for
different constructors, will result in a error messages being logged.

Change-Id: I3a31359c06b7452bfd973c3e5e54f9038acccfaa