pipe2bench2.c: use current dir instead of '/'

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
pipe2bench2.c: added pagecache flush, added multiple runs to make clear why test makes no sense :]

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
pipe2bench2.c: added output 'who is faster' :]

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>