check for existing kernel module built by dkms

From: Michael Prokop <mprokop@sipwise.com>

deployment.sh

@@ -938,7 +938,10 @@ EOT
 
   # we require those packages for dkms, so do NOT remove them:
   # binutils cpp-4.3 gcc-4.3-base linux-kbuild-2.6.32
-  if chroot $TARGET dkms status | grep ngcp-mediaproxy-ng ; then
+  if chroot $TARGET dkms status | grep -q ngcp-mediaproxy-ng ; then
+    if chroot $TARGET dkms status | grep -q '^ngcp-mediaproxy-ng.*: installed' ; then
+      echo "ngcp-mediaproxy-ng. kernel package already installed, skipping"
+    else
       # brrrr, don't tell this anyone or i'll commit with http://whatthecommit.com/ as commit msg!
       KERNELHEADERS=$(basename $(ls -d ${TARGET}/usr/src/linux-headers*amd64 | sort -u | head -1))
       if [ -z "$KERNELHEADERS" ] ; then
@@ -951,6 +954,7 @@ EOT
              -m ngcp-mediaproxy-ng -v $NGCPVERSION
       chroot $TARGET dkms install -k $KERNELVERSION -m ngcp-mediaproxy-ng -v $NGCPVERSION
     fi
+  fi
 
   # make sure all services are stopped
   for service in \