histogram: add a test case for bucket_sort_fn
histogram: add a test case for bucket_sort_fn

add a test case for bucket_sort_fn and show its
use scenario as well

mcaleavya/bcc,brendangregg/bcc,mcaleavya/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,mcaleavya/bcc,tuxology/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,brendangregg/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,mcaleavya/bcc,tuxology/bcc,tuxology/bcc