Fix debian-security mirror acccess error
Fix debian-security mirror acccess error

Security.debian.org accessing will actually access CDN mirror.
Some mirror should use "security.debian.org/debian-security"
like "mirror.xtom.com.hk", or it will cause apt-get update error[1].

[1]
E: Failed to fetch http://security.debian.org/dists/stretch/updates/main/binary-arm64/Packages 404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

Change-Id: Idd8b80c5f3c1e4aebd752e1ca6fb643e25eb1837

openstack/kolla,rahulunair/kolla,rahulunair/kolla,stackforge/kolla,stackforge/kolla,openstack/kolla,stackforge/kolla