Explicitly enable python support for debian.

Up until now we build only dummy not functioning python plugins
on Debian based systems. With the new build changes that means that the
plugins are no longer build as it only enables building of plugins that
actually do something.

debian/rules

@@ -36,6 +36,7 @@ override_dh_auto_configure:
   --with-bsrdir=/var/lib/bareos \
   --with-logdir=/var/log/bareos \
   --with-subsys-dir=/var/lock \
+  --with-python \
   --enable-smartalloc \
   --disable-conio \
   --enable-readline \