useradd.bbclass: print a warn when useradd not found

Exit quietly makes it very hard for debugging when user is not added as
expected, print a warning helps a lot.

(From OE-Core rev: 057885ed6f22781960bce4e082e3aa96e126764c)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/useradd.bbclass

@@ -118,6 +118,7 @@ useradd_sysroot () {
 	# useradd/groupadd tools are unavailable. If there is no dependency, we assume we don't want to
 	# create users in the sysroot
 	if ! command -v useradd; then
+		bbwarn "command useradd not found!"
 		exit 0
 	fi