CA-199734: code improvement on mapfn
CA-199734: code improvement on mapfn

The code change was suggested by Christian Lindig <christian.lindig@citrix.com>
for better naming and style.

Signed-off-by: Zheng Li <34c6fceca75e456f25e7e99531e2425c6c1de443@zheng.li>

jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api,jjd27/xen-api