MT#11455 Use install_sipwise_key for grml_debootstrap_upgrade

We already have a function which take care about the keys,
we should use it everywhere!

Moreover the public keys contains both release and autobuild keys already:
>> http://deb.sipwise.com/spce/sipwise.gpg
>> http://deb.sipwise.com/sppro/sipwise.gpg

> gpg sipwise.gpg
>> pub  1024D/A42C4F2A 2010-11-29 Sipwise GmbH (Sipwise repository key) <support@sipwise.com>
>> sub  2048g/680FBA8A 2010-11-29
>> pub  4096R/EE5E097D 2011-06-06 Sipwise autobuilder (Used to sign packages for autobuild) <development@sipwise.com>
>> sub  4096R/3A5C488C 2011-06-06

Change-Id: I8b729ff624954de0d133b803e4d220c29a4fd799

deployment.sh

@@ -211,9 +211,7 @@ grml_debootstrap_upgrade() {
     local debsrcfile=$(mktemp)
     echo "deb http://${SIPWISE_REPO_HOST}/grml.org grml-testing main" >> "$debsrcfile"
 
-    # the Sipwise deb.grml.org mirror is signed with 0xA42C4F2A (= 680FBA8A)
-    wget -O /etc/apt/680FBA8A.asc http://${SIPWISE_REPO_HOST}/autobuild/680FBA8A.asc
-    apt-key add /etc/apt/680FBA8A.asc
+    install_sipwise_key
 
     DEBIAN_FRONTEND='noninteractive' apt-get -o dir::cache="${TMPDIR}/cachedir" \
       -o dir::state="${TMPDIR}/statedir" -o dir::etc::sourcelist="$debsrcfile" \