core: add httpclient dependency to xmlrpc

java.lang.ClassNotFoundException:
org.apache.commons.httpclient.HttpException from [Module
"org.apache.xmlrpc:main" from local module loader @6633a290 (finder:
local module finder @47f5d05b (roots:
/usr/share/ovirt-engine/modules,/var/tmp/ovirt-engine/modules,/var/tmp/ovirt-engine/modules/system/layers/base))]

Change-Id: I566a2dbcac56bba1a81ef4b53b89750087d5776f
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>