mesa dispatch_sanity: call new functions to initialize exec table

mesa dispatch_sanity: call new functions to initialize exec table

In a future patch the exec functions will no longer set up
by _mesa_initialize_context and _vbo_CreateContext.

Therefore we must call _mesa_initialize_exec_table and
_mesa_initialize_exec_table_vbo.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>