Fix JWT auth test and alembic migration

A new version of pyjwt was released which alters an internal call
it makes to urllib which we have mocked in the unit tests.  Our
mock must be updated to match.

The previous version would call urlopen with a string url argument,
newer versions call it with a Request object (urllib accepts both).

This change updates the mock to accept both.

There has also been a recent alembic release which alters the function
signature of alter_column so that most arguments are now required to
be keyword arguments.  This causes one of our migrations to fail
since it was not passing the new type in as a positional argument.

Notably, the type was not the next positional argument in the
signature ("nullable" is), so this explains why we had two
"change patchset to string" migrations: the first one did not actually
work.

This change alters the migration to do what it effectively did rather
that what it was intended to do.  The later migration continues to
correct the error.

Change-Id: I10cdffa43147f7f72e431e7c64e10e9416dfb295

tests/unit/test_auth.py

@@ -70,6 +70,9 @@ def mock_get(url, params=None, **kwargs):
 
 
 def mock_urlopen(url, *args, **kwargs):
+    if hasattr(url, 'full_url'):
+        # Like a urllib.Request object
+        url = url.full_url
     if url == ("https://my.oidc.provider/auth/realms/realm-one/"
                "protocol/openid-connect/certs"):
         io = StringIO()

zuul/driver/sql/alembic/versions/cfc0dc45f341_change_patchset_to_string.py

@@ -17,11 +17,19 @@ import sqlalchemy as sa
 
 BUILDSET_TABLE = 'zuul_buildset'
 
+# Note: the following migration does not do what it was intended to do
+# (change the column type to a string).  It was introduced with an
+# error which instead caused the nullable flag to be set to true (even
+# though it was already set), effectively making it a no-op.  To
+# maintain compatibility with later versions of alembic, this has been
+# updated to explicitly do now what it implicitly did then.  A later
+# migration (19d3a3ebfe1d) corrects the error and changes the type.
+
 
 def upgrade(table_prefix=''):
     op.alter_column(table_prefix + BUILDSET_TABLE,
                     'patchset',
-                    sa.String(255),
+                    nullable=True,
                     existing_nullable=True,
                     existing_type=sa.Integer)