Retry on build_image failures and make sbt more aggressive by default

src/scripts/build_image

Index: src/scripts/build_image
diff --git a/src/scripts/build_image b/src/scripts/build_image
index 722a8ef62b9ca0f604bb8b62f403e47984917011..25dde2686bfd695981b69db95315164afb943db7 100755
--- a/src/scripts/build_image
+++ b/src/scripts/build_image
@@ -35,6 +35,8 @@ DEFINE_boolean installmask $FLAGS_TRUE \
   "Use INSTALL_MASK to shrink the resulting image."
 DEFINE_integer jobs -1 \
   "How many packages to build in parallel at maximum."
+DEFINE_integer retries -1 \
+  "On image mastering failure, the number of times to retry"
 DEFINE_boolean statefuldev $FLAGS_FALSE \
   "Install development packages on stateful partition rather than the rootfs"
 DEFINE_string to "" \
@@ -283,6 +285,11 @@ fi
 
 if [[ $FLAGS_jobs -ne -1 ]]; then
   EMERGE_JOBS="--jobs=$FLAGS_jobs"
+  if [[ $FLAGS_retries -eq -1 ]]; then
+    # The jobs flag can be flaky. Retry once by default,
+    # without the jobs flag.
+    FLAGS_retries=1
+  fi
 fi
 
 # Prepare stateful partition with some pre-created directories
@@ -305,7 +312,7 @@ sudo mount --bind "${STATEFUL_DIR}/var" "${ROOT_FS_DIR}/var"
 # runtime packages for chrome os. This builds up a chrome os image from binary
 # packages with runtime dependencies only.  We use INSTALL_MASK to trim the
 # image size as much as possible.
-sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
+eretry sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
   --root="$ROOT_FS_DIR" --root-deps=rdeps \
   --usepkgonly chromeos $EMERGE_JOBS
 
@@ -315,7 +322,7 @@ ROOT_DEV_DIR="$ROOT_FS_DIR"
 
 # Install development packages.
 if [[ $FLAGS_withdev -eq $FLAGS_TRUE ]] ; then
-  sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
+  eretry sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
       --root="$ROOT_DEV_DIR" --root-deps=rdeps \
       --usepkgonly chromeos-dev $EMERGE_JOBS
 
@@ -324,14 +331,14 @@ if [[ $FLAGS_withdev -eq $FLAGS_TRUE ]] ; then
 fi
 
 if [ -n "$FLAGS_factory_server" ]; then
-  sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
+  eretry sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
       --root="$ROOT_DEV_DIR" --root-deps=rdeps \
       --usepkgonly chromeos-factoryinstall $EMERGE_JOBS
 fi
 
 # Install packages required for testing.
 if [[ $FLAGS_withtest -eq $FLAGS_TRUE ]] ; then
-  sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
+  eretry sudo INSTALL_MASK="$INSTALL_MASK" emerge-${BOARD} \
       --root="$ROOT_DEV_DIR" --root-deps=rdeps \
       --usepkgonly chromeos-test $EMERGE_JOBS
 fi