MT#4469 Use arch=amd64 for Debian package repository

We don't have any other architectures besides the amd64 one on
our own repositories and nowadays with MultiArch people might have
e.g. i386 enabled (via 'dpkg --add-architecture i386'), resulting
in errors like:

| W: Failed to fetch http://deb.sipwise.com/spce/3.0/dists/wheezy/main/binary-i386/Packages [^] 404 Not Found
| W: Failed to fetch http://deb.sipwise.com/wheezy-backports/dists/wheezy-backports/main/binary-i386/Packages [^] 404 Not Found
| E: Some index files failed to download. They have been ignored, or old ones used instead.

Avoid retrieval of i386 Packages files by limiting the deb entry
to the amd64 architecture.

deployment.sh

@@ -1106,10 +1106,10 @@ deb http://security.debian.org/ ${DEBIAN_RELEASE}/updates main
 deb http://ftp.debian.org/debian ${DEBIAN_RELEASE}-updates main
 
 # Sipwise repositories
-deb http://deb.sipwise.com/autobuild/release/release-${AUTOBUILD_RELEASE} release-${AUTOBUILD_RELEASE} main
+deb [arch=amd64] http://deb.sipwise.com/autobuild/release/release-${AUTOBUILD_RELEASE} release-${AUTOBUILD_RELEASE} main
 
 # Sipwise ${DEBIAN_RELEASE} backports
-deb http://deb.sipwise.com/${DEBIAN_RELEASE}-backports/ ${DEBIAN_RELEASE}-backports main
+deb [arch=amd64] http://deb.sipwise.com/${DEBIAN_RELEASE}-backports/ ${DEBIAN_RELEASE}-backports main
 
 EOF
   fi