hard-code status in invitation status migration

alembic/versions/e1081cf01780_adjust_invitation_status.py

@@ -7,10 +7,8 @@ Create Date: 2018-11-01 12:24:10.970963
 """
 from alembic import op
 import sqlalchemy as sa
-from atst.models.invitation import Status
 from enum import Enum
 
-
 # revision identifiers, used by Alembic.
 revision = 'e1081cf01780'
 down_revision = 'a9d8c6b6221c'
@@ -18,6 +16,13 @@ branch_labels = None
 depends_on = None
 
 
+class Status(Enum):
+    ACCEPTED = "accepted"
+    REVOKED = "revoked"
+    PENDING = "pending"
+    REJECTED_WRONG_USER = "rejected_wrong_user"
+    REJECTED_EXPIRED = "rejected_expired"
+
 def upgrade():
     conn = op.get_bind()
     constraints = ", ".join(["'{}'::character varying::text".format(s.name) for s in Status])