Migrate mistral task_type

In order to be able to get full info from the API for old tasks,
it is needed to get the type from the spec column to the type column.

The alternative was adding a release note explaining the inconsistency.

Change-Id: I48dd286f749ceb491ab32ee15af62a8db54acdc7
(cherry picked from commit 4f07468bc8)

mistral/db/sqlalchemy/migration/alembic_migrations/versions/020_add_type_to_task_execution.py

@@ -0,0 +1,73 @@
+# Copyright 2016 OpenStack Foundation.
+#
+# 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 type to task execution
+
+Revision ID: 020
+Revises: 019
+Create Date: 2016-10-05 13:24:52.911011
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '020'
+down_revision = '019'
+
+from alembic import op
+from mistral.db.sqlalchemy import types as st
+import sqlalchemy as sa
+
+# A simple model of the task executions table with only the fields needed for
+# the migration.
+task_executions = sa.Table(
+    'task_executions_v2',
+    sa.MetaData(),
+    sa.Column('id', sa.String(36), nullable=False),
+    sa.Column(
+        'spec',
+        st.JsonMediumDictType()
+    ),
+    sa.Column('type', sa.String(10), nullable=True)
+)
+
+
+def upgrade():
+
+    op.add_column(
+        'task_executions_v2',
+        sa.Column('type', sa.String(length=10), nullable=True)
+    )
+
+    session = sa.orm.Session(bind=op.get_bind())
+    values = []
+
+    for row in session.query(task_executions):
+        values.append({'id': row[0],
+                       'spec': row[1]})
+
+    with session.begin(subtransactions=True):
+        for value in values:
+            task_type = "ACTION"
+            if "workflow" in value['spec']:
+                task_type = "WORKFLOW"
+
+            session.execute(
+                task_executions.update().values(type=task_type).where(
+                    task_executions.c.id == value['id']
+                )
+            )
+
+    # this commit appears to be necessary
+    session.commit()