apt_key: fix spurious failure to import a subkey (#4366)

Importing a (sign only) subkey with apt_key module always fails,
however the actual keyring gets created and contains the correct keys.
Apparently the all_keys function skips the subkeys, hence the problem.

Fixes #4365

lib/ansible/modules/packaging/os/apt_key.py

@@ -132,7 +132,7 @@ def all_keys(module, keyring, short_format):
     results = []
     lines = out.split('\n')
     for line in lines:
-        if line.startswith("pub"):
+        if line.startswith("pub") or line.startswith("sub"):
             tokens = line.split()
             code = tokens[1]
             (len_type, real_code) = code.split("/")