propertydialog adjustments for package.bbclass

After moving the code from packageinfo.bbclass to
package.bbclass, minor adjustments were made to the
parsing of the package items.

Signed-off-by: Andrei Dinu <andrei.adrianx.dinu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>