caps: Modify memory units of numa node

This patch modifies the reported memory units in numa node collection
process. In order to avoid the limitation of xmlrpc, the memory values
are modified to string format in MiB unit.

Change-Id: Ibf59a940395cc9d6134503826552fe16053a76f8
Signed-off-by: Bruce Shi <xiao-lei.shi@hp.com>
Reviewed-on: http://gerrit.ovirt.org/27399
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>