TT#23964 Use deb.debian.org as debian mirror

Stretch based amazon image has cdn-aws.deb.debian.org as debian mirror.
It fails very often with 503 http error. For previous amazon
jessie-based images different mirror cloudfront.debian.net was used
and it didn't fail even though they both terminate via/on
cloudfront.net. Let's use deb.debian.org instead.

Change-Id: I100a79e2e6fe4c1766b93586166aa29d1b48d543

ec2-create-ce

@@ -321,6 +321,7 @@ cat > "$USER_DATA_FILE" << EOF
 #!/bin/bash
 wget -O /tmp/ngcp-installer.deb http://deb.sipwise.com/spce/ngcp-installer-${NGCP_RELEASE}.deb
 dpkg -i /tmp/ngcp-installer.deb
+sed -i 's/cdn-aws.deb.debian.org/deb.debian.org/' /etc/apt/sources.list
 
 if [ -d /run/systemd/system ] ; then
   echo "Switching from systemd to sysvinit (pre-reboot)"