Add non-model index names to autogen exclude filters

Add non-model index names to autogen exclude filters

The SQLAlchemy MySQL dialect generates implicit indexes
in the less-common case of an integer column within a composite
primary key where autoincrement is not set to False.
Add a rule to ignore these indexes when performing
autogenerate against a target database.

Change-Id: I49abb3f7ad9731cde046fa2862cdb9ec16c3aeb3
Partially-Implements: blueprint online-schema-migrations