Update build script to run in container

Bug: N/A
Test: run kokoro
Change-Id: Ie83204d4ea4630bf3b6783f1605f451082d1051f
diff --git a/build/debian/build.sh b/build/debian/build.sh
index e7e44f2..24de78a 100755
--- a/build/debian/build.sh
+++ b/build/debian/build.sh
@@ -53,6 +53,8 @@
 		udev \
 		qemu-system-arm \
 		qemu-user-static
+
+        sed -i s/losetup\ -f/losetup\ -P\ -f/g /usr/sbin/fai-diskimage
 }
 
 download_debian_cloud_image() {