testing: Update base image to Debian jessie

Several packages got renamed/updated, libgcrypt was apparently installed
by default previously.

Since most libraries changed we have to completely rebuild all the tools
installed in the root image.  We currently don't provide a clean target in
the recipes, and even if we did we'd have to track which base image we
last built for.  It's easier to just use a different build directory for
each base image, at the cost of some additional disk space (if not manually
cleaned).  However, that's also the case when updating kernel or
software versions.

testing/testing.conf

@@ -35,8 +35,6 @@ fi
 
 # Build directory where the guest kernel and images will be built
 : ${BUILDDIR=$TESTDIR/build}
-# Directory shared between host and guests
-: ${SHAREDDIR=$BUILDDIR/shared}
 
 # Logfile
 : ${LOGFILE=$BUILDDIR/testing.log}
@@ -50,12 +48,15 @@ fi
 
 # Base image settings
 # The base image is a pristine OS installation created using debootstrap.
-: ${BASEIMGSIZE=1400}
-: ${BASEIMGSUITE=wheezy}
+: ${BASEIMGSIZE=1600}
+: ${BASEIMGSUITE=jessie}
 : ${BASEIMGARCH=amd64}
 : ${BASEIMG=$IMGDIR/debian-$BASEIMGSUITE-$BASEIMGARCH.$IMGEXT}
 : ${BASEIMGMIRROR=http://http.debian.net/debian}
 
+# Directory shared between host and guests
+: ${SHAREDDIR=$BUILDDIR/shared/$BASEIMGSUITE}
+
 # Root image settings
 # The root image is the origin of all guest images. It is a clone of the base
 # image and contains additional test-specific software and patches.