alembic: guard against config.py not existing yet

one of the quirks of SecureDrop is that config.py might
not yet exist until the app Ansible role has ran

this means for fresh installs, the database must be created
via alembic upgrade head without any errors raising, else
the securedrop-app-code package install will fail

securedrop/alembic/versions/3da3fcab826a_delete_orphaned_submissions.py

@@ -7,15 +7,24 @@
 Create Date: 2018-11-25 19:40:25.873292
 
 """
+import os
 from alembic import op
 import sqlalchemy as sa
 from journalist_app import create_app
-from models import Submission, Reply
 from rm import srm
-from sdconfig import config
 from store import NoFileFoundException, TooManyFilesException
 from worker import rq_worker_queue
 
+# raise the errors if we're not in production
+raise_errors = os.environ.get("SECUREDROP_ENV", "prod") != "prod"
+
+try:
+    from sdconfig import config
+except ImportError:
+    # This is a fresh install, and config.py has not been created yet.
+    if raise_errors:
+        raise
+
 # revision identifiers, used by Alembic.
 revision = '3da3fcab826a'
 down_revision = 'a9fe328b053a'
@@ -42,51 +51,55 @@ def upgrade():
         sa.text(raw_sql_grab_orphaned_objects('replies'))
     ).fetchall()
 
-    app = create_app(config)
-    with app.app_context():
-        for submission in submissions:
-            try:
-                conn.execute(
-                sa.text("""
-                    DELETE FROM submissions
-                    WHERE id=:id
-                """).bindparams(id=submission.id)
-                )
-
-                file_path = app.storage.path_without_filesystem_id(submission.filename)
-                rq_worker_queue.enqueue(srm, file_path)
-            except NoFileFoundException:
-                # The file must have been deleted by the admin, remove the row
-                conn.execute(
-                sa.text("""
-                    DELETE FROM submissions
-                    WHERE id=:id
-                """).bindparams(id=submission.id)
-                )
-            except TooManyFilesException:
-                pass
-
-        for reply in replies:
-            try:
-                conn.execute(
+    try:
+        app = create_app(config)
+        with app.app_context():
+            for submission in submissions:
+                try:
+                    conn.execute(
                     sa.text("""
-                        DELETE FROM replies
+                        DELETE FROM submissions
                         WHERE id=:id
-                    """).bindparams(id=reply.id)
-                )
-
-                file_path = app.storage.path_without_filesystem_id(reply.filename)
-                rq_worker_queue.enqueue(srm, file_path)
-            except NoFileFoundException:
-                # The file must have been deleted by the admin, remove the row
-                conn.execute(
+                    """).bindparams(id=submission.id)
+                    )
+
+                    file_path = app.storage.path_without_filesystem_id(submission.filename)
+                    rq_worker_queue.enqueue(srm, file_path)
+                except NoFileFoundException:
+                    # The file must have been deleted by the admin, remove the row
+                    conn.execute(
                     sa.text("""
-                        DELETE FROM replies
+                        DELETE FROM submissions
                         WHERE id=:id
-                    """).bindparams(id=reply.id)
-                )
-            except TooManyFilesException:
-                pass
+                    """).bindparams(id=submission.id)
+                    )
+                except TooManyFilesException:
+                    pass
+
+            for reply in replies:
+                try:
+                    conn.execute(
+                        sa.text("""
+                            DELETE FROM replies
+                            WHERE id=:id
+                        """).bindparams(id=reply.id)
+                    )
+
+                    file_path = app.storage.path_without_filesystem_id(reply.filename)
+                    rq_worker_queue.enqueue(srm, file_path)
+                except NoFileFoundException:
+                    # The file must have been deleted by the admin, remove the row
+                    conn.execute(
+                        sa.text("""
+                            DELETE FROM replies
+                            WHERE id=:id
+                        """).bindparams(id=reply.id)
+                    )
+                except TooManyFilesException:
+                    pass
+    except:  # noqa
+        if raise_errors:
+            raise
 
 
 def downgrade():