More robust fetching - try twice after random delay

Signed-off-by: Michal Hrusecky <michal.hrusecky@nic.cz>

compile_fw

@@ -206,7 +206,7 @@ update_mirror() {
 	cd "$GIT_MIRROR"
 	OPENWRT_URL="$GIT_MIRROR/openwrt"
 	for mirror in ./*; do
-		cd "$mirror" && git fetch --all
+		cd "$mirror" && { git fetch --all || { sleep $(( 1 + $RANDOM % 10 )); git fetch --all  } }
 		cd "$GIT_MIRROR"
 	done
 	popd