Add fakesrc ! fakesink test

Add fakesrc and fakesink and some performance test
Small cleanups

spa/plugins/test/meson.build

@@ -0,0 +1,9 @@
+test_sources = ['fakesrc.c', 'fakesink.c', 'plugin.c']
+
+testlib = shared_library('spa-test',
+                          test_sources,
+                          include_directories : [ spa_inc, spa_libinc],
+                          dependencies : threads_dep,
+                          link_with : spalib,
+                          install : true,
+                          install_dir : '@0@/spa'.format(get_option('libdir')))