The semisync plugin library names on Unix like systems were prefixed with
'lib', which did not follow the conventions.

Fix the problem by removing the 'lib' prefix on Unix systems.


mysql-test/mysql-test-run.pl:
  Remove 'lib' prefix for semisync plugin library names
plugin/semisync/Makefile.am:
  Remove 'lib' prefix for semisync plugin library names
plugin/semisync/plug.in:
  Remove 'lib' prefix for semisync plugin library names