TEST: add a progam to compare the speed of vsnprintf and qb_vsnprintf_serialize

On my system I get:

qb store] Duration:     8.289 OPs/sec: 1206381.250
snprintf] Duration:    16.712 OPs/sec: 598368.000

Signed-off-by: Angus Salkeld <asalkeld@redhat.com>