XenAPI: Fix netwrap to support security group

XenAPI: Fix netwrap to support security group

This implementation is to give support on neutron security group with
XenServer as compute driver. When using openvswitch, the ovs agent on
compute node cannot execute some linux commands correctly due to
xenserver driver lacking of such support. This change will add some
allowed commands which can be executed in dom0.

Implements: blueprint xenserver-give-support-on-neutron-security-group

Change-Id: I377f8ad51e1d2725c3e0153e64322055fcce7b54