webadmin: Optimize iteration over map (Findbugs)

Replaced the iteration over the map keys with an iteration over its
entries, as a response to Findbugs warning WMI_WRONG_MAP_ITERATOR.

Change-Id: I767b72fecfb8ec76d9c259f1b059c243ecf421fb
Signed-off-by: Lior Vernia <lvernia@redhat.com>