tests: printf: add unit test for %%
tests: printf: add unit test for %%

https://bugzilla.gnome.org/show_bug.cgi?id=748414

krichter722/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,mparis/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,krichter722/gstreamer,krichter722/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,jpxiong/gstreamer,centricular/gstreamer,centricular/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer