Add move_surface wfits test extension.

This adds a new wfits interface called "wfits_manip" which will
allow tests to manipulate certain server-side state.  Currently
this interface defines one method to move surfaces to a specific
position on the output.  This will allow tests to ensure surfaces
are in deterministic positions so they can avoid various corner-case
surface position selections by the compositor.  For example, avoid
two surfaces from being overlapped or avoid surfaces mapped near
the edge of the compositor output geometry; both which can
interfere with certain test situations.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>
core: fix MultiResourceTest intermittent failure

The MultiResourceTest would fail occassionally when the test
surfaces got placed near the edges of the compositor output
or when the surfaces were overlapped.  Weston's shell places
surfaces in random positions, thus to avoid hitting the above
corner-cases we just position them explicitly with the wfits_manip
test extension.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>