tests: Define and implement a test protocol extension.

tests: Define and implement a test protocol extension.

The weston test extension, called weston-test.so, can be loaded
from the "modules" configuration option on the command line
or in the .ini file.

Clients can bind to the "wl_test" interface to interact with
the weston test extension.

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