Midonet Plugin bugfixes

* Updated SQL upgrade scripts to include midonet configs.
* Fixed bug where default ICMP allow rule was missing
  on static NAT creation, keeping VMs from being able
  to ping the gateway.
* Changed the filter in the MidoNetElement callbacks to allow
  calls when Midonet is configured.

Signed-off-by: Hugo Trippaers <htrippaers@schubergphilis.com>
CLOUDSTACK-962: Because of the same reason to this (CLOUDSTACK-685)
https://reviews.apache.org/r/11157/

Signed-off-by: Chip Childers <chip.childers@gmail.com>