MT#6265 Always update chroot before trying to install additional packages

Even if our own key is already installed the package list might
not be up2date yet (e.g. for wheezy-backports):

| The following NEW packages will be installed:
|   linux-compiler-gcc-4.6-x86 linux-headers-3.13-0.bpo.1-amd64
|   linux-headers-3.13-0.bpo.1-common linux-kbuild-3.13
| The following packages will be upgraded:
|   linux-headers-amd64
| 1 upgraded, 4 newly installed, 0 to remove and 1 not upgraded.
| Need to get 5187 kB of archives.
| After this operation, 32.9 MB of additional disk space will be used.
| WARNING: The following packages cannot be authenticated!
|   linux-compiler-gcc-4.6-x86 linux-headers-3.13-0.bpo.1-common
|   linux-kbuild-3.13 linux-headers-3.13-0.bpo.1-amd64 linux-headers-amd64

deployment.sh

@@ -1752,9 +1752,11 @@ vagrant_configuration() {
     echo "Installing Sipwise Debian mirror key (680FBA8A)."
     grml-chroot "${TARGET}" wget -O /etc/apt/680FBA8A.asc http://deb.sipwise.com/autobuild/680FBA8A.asc
     grml-chroot "${TARGET}" apt-key add /etc/apt/680FBA8A.asc
-    grml-chroot "${TARGET}" apt-get update
   fi
 
+  # make sure we use the most recent package versions, including apt-key setup
+  grml-chroot "${TARGET}" apt-get update
+
   # bzip2, linux-headers-amd64 and make are required for VirtualBox Guest Additions installer
   # less + sudo are required for Vagrant itself
   echo "Installing software for VirtualBox Guest Additions installer"