Fix usage of dict.keys in apiclient.exceptions

Method dict.keys returns a dict_keys object in Python 3, which is
not indexable, so we get exception TypeError ('dict_keys' object does not
support indexing). This is fix of usage dict object in module exceptions.

Related to bp make-python3-compatible

Change-Id: Ie827f408cd23d4baa900f2ae1b074d13a5cd6f0e
Merge "Fix usage of dict.keys in apiclient.exceptions"