[client] add GPG_ALLOW_NO_SIGNING_PW and --gpg-no-signing-pw

[client] add GPG_ALLOW_NO_SIGNING_PW and --gpg-no-signing-pw

This change brings similar functionality to the client as the GPG_ALLOW_NO_PW
keyword in the server access.conf file.  Although this option is less likely
to be used than the analogous server functionality, it stands to reason that
the client should offer this feature.  The test suite has also been updated to
not use the --get-key option for the 'no password' GPG tests.