crowbar-pacemaker: Increase tune.bufsize option of haproxy

The default value (16384) is too small for keystone: getting a PKI token
from its ID fails with a 400 Bad Request message from haproxy because
the URI path is too long.
(cherry picked from commit de4b60e0bf94c3559de723e07dd4a1d139684b96)
haproxy: Allow setting the tune.bufsize and tune.chksize options
(cherry picked from commit ae3818723e0b38a690a6fabd3d390daafcfce961)