Handle missing lsb_release

The lsb-release package isn't a stated dependency and isn't present on
a minimal Debian install.

debian/util.sh

@@ -386,9 +386,13 @@ build_all () {
   shift $(($OPTIND-1))
   [ -n "$archs" ] || archs="amd64 i386"
   if [ -z "$distros" ]; then
+    local default_distros="sid jessie wheezy"
+    if [ -z "$(which lsb_release)" ]; then
+      distros="$default_distros"
+    else
       case "$(lsb_release -is)" in
         Debian)
-        distros="sid jessie wheezy"
+          distros="$default_distros"
           ;;
         Ubuntu)
           distros="utopic trusty"
@@ -399,6 +403,7 @@ build_all () {
           ;;
       esac
     fi
+  fi
   ! $depinst || aptitude install -y \
     rsync git less cowbuilder ccache \
     devscripts equivs build-essential