Add artifact table

Add an artifact table to the SQL reporter, and allow builds to store
artifact URLs using zuul_return.  The web API will return the urls.

Change-Id: I8adfc25cc93327ca73c98bbe170e8f39a0864f7f

zuul/driver/sql/alembic/versions/ea2bae776723_add_artifact_table.py

@@ -0,0 +1,47 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+"""add_artifact_table
+
+Revision ID: ea2bae776723
+Revises: f181b33958c6
+Create Date: 2018-11-26 14:48:54.463512
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'ea2bae776723'
+down_revision = 'f181b33958c6'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+ARTIFACT_TABLE = 'zuul_artifact'
+BUILD_TABLE = 'zuul_build'
+
+
+def upgrade(table_prefix=''):
+    op.create_table(
+        table_prefix + ARTIFACT_TABLE,
+        sa.Column('id', sa.Integer, primary_key=True),
+        sa.Column('build_id', sa.Integer,
+                  sa.ForeignKey(table_prefix + BUILD_TABLE + ".id")),
+        sa.Column('name', sa.String(255)),
+        sa.Column('url', sa.TEXT()),
+    )
+
+
+def downgrade():
+    raise Exception("Downgrades not supported")