classes: Add mechanism to install packages into images only if they've been built

meta/classes/image.bbclass

@@ -9,6 +9,7 @@ INHIBIT_DEFAULT_DEPS = "1"
 # "export IMAGE_BASENAME" not supported at this time
 IMAGE_BASENAME[export] = "1"
 export PACKAGE_INSTALL ?= "${IMAGE_INSTALL}"
+PACKAGE_INSTALL_ATTEMPTONLY ?= ""
 
 # We need to recursively follow RDEPENDS and RRECOMMENDS for images
 do_rootfs[recrdeptask] += "do_deploy do_populate_staging"
@@ -36,6 +37,7 @@ python () {
     bb.data.setVarFlag('do_rootfs', 'depends', deps, d)
 
     runtime_mapping_rename("PACKAGE_INSTALL", d)
+    runtime_mapping_rename("PACKAGE_INSTALL_ATTEMPTONLY", d)
 }
 
 #