Use mysql LONGTEXT for atomdetails results

With a lot of possible retries using mysql sa.Text for result field
atomdetails table is not enough.

Updated 'results' column type to LONGTEXT in mysql backend case.

PosgreSQL seems not to be affected as postgres text type is not
having length limitation.

Co-Authored-By: Michael Johnson <johnsomor@gmail.com>

Change-Id: I4e44e3288ae49d85c5b5ce8ff26ba83f3b9d2c7b
Closes-bug: #1838015

taskflow/persistence/backends/sqlalchemy/alembic/versions/0bc3e1a3c135_set_result_meduimtext_type.py

@@ -0,0 +1,43 @@
+#    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.
+
+"""set_result_meduimtext_type
+
+Revision ID: 0bc3e1a3c135
+Revises: 2ad4984f2864
+Create Date: 2019-08-08 16:11:36.221164
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '0bc3e1a3c135'
+down_revision = '2ad4984f2864'
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import mysql
+
+
+def upgrade():
+    bind = op.get_bind()
+    engine = bind.engine
+    if engine.name == 'mysql':
+        op.alter_column('atomdetails', 'results', type_=mysql.LONGTEXT,
+                        existing_nullable=True)
+
+
+def downgrade():
+    bind = op.get_bind()
+    engine = bind.engine
+    if engine.name == 'mysql':
+        op.alter_column('atomdetails', 'results', type_=sa.Text(),
+                        existing_nullable=True)