classes/packageinfo: use better method to check if package exists

classes/packageinfo: use better method to check if package exists

Instead of using a rather error-prone method of looking for output
package files in order to determine if a package got created, use the
.packaged file within pkgdata.

This fixes two separate issues:
* Some packages apparently not being found by this code e.g. all
  apm/apmd packages when using ipk packaging.
* Buggy implementation of this checking code which triggered an
  exception during the event handler if PKGV was overridden on a
  per-package basis (as it is with external-sourcery-toolchain), which
  blocked Hob from completing parsing at 99% - fixes [YOCTO #2651].

(From OE-Core rev: 48169c6bc44c546cecaa06207b6c36da558b81f7)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>