package_manager/ipk: give out useful reason about an unmatched package

package_manager/ipk: give out useful reason about an unmatched package

Give out useful information when a package could not be matched.

Before the change:

  error: opkg_solver_install: No candidates to install catch2 (null)!

With this patch:

  error: opkg_solver_install: No candidates to install catch2 (null)!
  ...
  catch2 is a recipe. Its generated packages are: ['catch2-src', 'catch2-dbg', 'catch2-staticdev', 'catch2-dev', 'catch2-doc']
  Either specify a generated package or set ALLOW_EMPTY:${PN} = "1" in catch2 recipe

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>