Use parallel syncs.

Also, wait until syncing is done to write the tree.
Also, only delete the out tree.

Change-Id: I7d6c144c8ea5a702b74c827dd5879107baa4c145
diff --git a/generate-blob-lists.sh b/generate-blob-lists.sh
index 3977571..02323b2 100755
--- a/generate-blob-lists.sh
+++ b/generate-blob-lists.sh
@@ -45,9 +45,9 @@
 DEVICES="crespo crespo4g stingray wingray panda toro torospr maguro"
 export LC_ALL=C
 
-repo sync
-repo sync
-repo sync
+repo sync -j32 -n
+repo sync -j32 -n
+repo sync -j2 -l
 
 ARCHIVEDIR=archive-$(date +%s)
 if test -d archive-ref
@@ -120,7 +120,10 @@
   fi
 done
 
-if ! test -d archive-ref
+if true
+then
+  rm -rf out/
+elif ! test -d archive-ref
 then
   echo * device/* |
     tr \  \\n |