sign_rpm.bbclass: do not store key details in signer instance
Refactor the LocalSigner class. Do not store keyid or passphrase file in
the signer object as they are only needed for some of the methods. For
example, the newly added verify() method does not need any key
parameters and export_pubkey only uses keyid.
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
