Replace usage of google.api.core with google.api_core (#4221)

* Remove api.core packages from google.cloud.core, make google.cloud.core depend on api_core.

* s/google.api.core/google.api_core/g and nox updates

* Fixing core tests, addressing review feedback

* Fix bigquery

packages/google-cloud-trace/google/cloud/trace/_gax.py

@@ -14,7 +14,7 @@
 
 """GAX Wrapper for interacting with the Stackdriver Trace API."""
 
-from google.api.core import page_iterator
+from google.api_core import page_iterator
 from google.cloud.gapic.trace.v1 import trace_service_client
 from google.cloud.proto.devtools.cloudtrace.v1 import trace_pb2
 from google.gax import CallOptions
@@ -131,7 +131,7 @@ def list_traces(
                            passed, the API will return the first page of
                            entries.
 
-        :rtype: :class:`~google.api.core.page_iterator.Iterator`
+        :rtype: :class:`~google.api_core.page_iterator.Iterator`
         :returns: Traces that match the specified filter conditions.
         """
         if page_token is None:
@@ -170,7 +170,7 @@ def _parse_trace_pb(trace_pb):
 def _item_to_mapping(iterator, trace_pb):
     """Helper callable function for the GAXIterator
 
-    :type iterator: :class:`~google.api.core.page_iterator.Iterator`
+    :type iterator: :class:`~google.api_core.page_iterator.Iterator`
     :param iterator: The iterator that is currently in use.
 
     :type trace_pb: :class:`google.cloud.proto.devtools.cloudtrace.v1.

packages/google-cloud-trace/google/cloud/trace/client.py

@@ -148,7 +148,7 @@ def list_traces(
                            passed, the API will return the first page of
                            entries.
 
-        :rtype: :class:`~google.api.core.page_iterator.Iterator`
+        :rtype: :class:`~google.api_core.page_iterator.Iterator`
         :returns: Traces that match the specified filter conditions.
         """
         if project_id is None:

packages/google-cloud-trace/nox.py

@@ -19,7 +19,10 @@
 import nox
 
 
-LOCAL_DEPS = ('../core/',)
+LOCAL_DEPS = (
+    os.path.join('..', 'api_core'),
+    os.path.join('..', 'core'),
+)
 
 
 @nox.session