oe-selftest-image: use explicit IMAGE_FEATURES instead of debug-tweaks

debug-tweaks is vague and doesn't give any indication that the root user
can login over SSH without a password.  This behaviour is incredibly
dangerous if used unwittingly, so discourage it by using the underlying
features explicitly to spell out exactly what is being done.

(From OE-Core rev: 83cd8b5ca4544e9b19c110035276e5de2ebe7404)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-selftest/recipes-test/images/oe-selftest-image.bb

@@ -2,7 +2,7 @@ SUMMARY = "An image used during oe-selftest tests"
 
 # libudev is needed for deploy mdadm via devtool
 IMAGE_INSTALL = "packagegroup-core-boot packagegroup-core-ssh-dropbear libudev"
-IMAGE_FEATURES = "debug-tweaks"
+IMAGE_FEATURES = "allow-empty-password empty-root-password allow-root-login"
 
 IMAGE_LINGUAS = " "