Heal virt-host using guest products and only virt_limit pools

When autohealing a virtual guest, first attempt to heal the host.
However, when we heal the host, we only want to use pools that provide
subpools accessable by the guest, for the guests installed products, not
necessarily what the host machine has installed.
Merge pull request #408 from candlepin/ckozak/heal_host_virt_limit

heal host with only virt_limit subs