Fix umount issue on Ubuntu20.04

When update Ubuntu version to 20.04, After first  gbs build, for some kind reason
During the second gbs build , it will have umount issue:
error: there're mounted directories to build root. Please unmount them manually to avoid being deleted unexpectly:
    / ==> ~/GBS-ROOT/XXX/local/BUILD-ROOTS/scratch.armv7l.0/proc/sys/fs/binfmt_misc
So using umount option -l for lazy umount can fix this issue.
Change-Id: I5f4ea680fefcc38cd9dce30dfa458710c086a399
Signed-off-by: biao716.wang <biao716.wang@samsung.com>

diff --git a/common_functions b/common_functions
index 8512eae..f0084f8 100755 (executable)
--- a/common_functions
+++ b/common_functions
@@ -151,7 +151,7 @@ buildroot_umount() {
     # XXX: use stat -f /dev/pts/ -c %T  to check whether it's mounted and not suppress errors?
     local LOOP_CNT=1
     while [ $LOOP_CNT -le 20 ] ; do
-        umount -n "$BUILD_ROOT/$d" 2>/dev/null
+        umount -n -l "$BUILD_ROOT/$d" 2>/dev/null
         if test $? -ne 0; then
             break
         fi