Make byte_count on BlobUpload table not nullable

The byte_count field on the BlobUpload model is marked as not
nullable, but the migration to make the field a big integer removed
that restriction (#2388 :: 76de324) in the database.  It's still in
the model though, which means they are out of sync.  This adds a
migration to mark the field as not nullable in the database again.

data/migrations/versions/152edccba18c_make_blodupload_byte_count_not_nullable.py

@@ -0,0 +1,24 @@
+"""Make BlodUpload byte_count not nullable
+
+Revision ID: 152edccba18c
+Revises: c91c564aad34
+Create Date: 2018-02-23 12:41:25.571835
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '152edccba18c'
+down_revision = 'c91c564aad34'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade(tables):
+    op.alter_column('blobupload', 'byte_count', existing_type=sa.BigInteger(),
+                    nullable=False)
+
+
+def downgrade(tables):
+    op.alter_column('blobupload', 'byte_count', existing_type=sa.BigInteger(),
+                    nullable=True)