feature(keyringctl): verify file structure integrity and packets

This moves all verify code to an own module and adds support to check
all packet files in the structure for integrity. This is done by parsing
assumptions like packet kind, type, issuer and location etc.

libkeyringctl/cli.py

@@ -15,9 +15,9 @@ from .keyring import convert
 from .keyring import export
 from .keyring import inspect_keyring
 from .keyring import list_keyring
-from .keyring import verify
 from .util import absolute_path
 from .util import cwd
+from .verify import verify
 
 parser = ArgumentParser()
 parser.add_argument(