image.bbclass: Add package-management image feature to validitems

Some images dont use core-image bbclass and add this feature directly

Fixes parsing errors like

/builds1/angstrom/cache/prserv.sqlite3, IP: 127.0.0.1, PORT: 34734, PID:
24551 Parsing recipes...ERROR: Unable to parse /builds1/angstrom/sources/meta-kde/recipes-images/angstrom-kde-desktop-imag e.bb: Exited with "1" ERROR: 'package-management' in IMAGE_FEATURES is not a
valid image feature. Valid features: dbg-pkgs debug-tweaks dev-pkgs doc-pkgs ptest-pkgs read-only-rootfs splash staticdev-pkgs ERROR:
'package-management' in IMAGE_FEATURES is not a valid image feature. Valid
features: dbg-pkgs debug-tweaks dev-pkgs doc-pkgs ptest-pkgs read-only-rootfs splash staticdev-pkgs ERROR: Command execution failed:
Exited with 1

---
 meta/classes/image.bbclass |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 2b42e12..4f07708 100644
@@ -19,7 +19,7 @@ INHIBIT_DEFAULT_DEPS = "1"
 # IMAGE_FEATURES may contain any available package group
 IMAGE_FEATURES ?= ""
 IMAGE_FEATURES[type] = "list"
-IMAGE_FEATURES[validitems] += "debug-tweaks read-only-rootfs"
+IMAGE_FEATURES[validitems] += "debug-tweaks read-only-rootfs package-management"
 
 # rootfs bootstrap install
 ROOTFS_BOOTSTRAP_INSTALL = "${@base_contains("IMAGE_FEATURES", "package-management", "", "${ROOTFS_PKGMANAGE_BOOTSTRAP}",d)}"

1.7.9.5