Add sqlalchemy migration utils.check_shadow_table method

This method check that our table with name `xxx`:
1) Has shadow table `shadow_xxx`
2) All columns in `xxx` are also in `shadow_xxx` (with same type)
3) There is no extra columns in `shadow_xxx`

Will be used to check that all shadow tables are up-to-date.

blueprint db-improve-archiving

Change-Id: I0b366afe1b7d8703ab9c49a68977202b82d844fc
Add sqlalchemy migration utils.create_shadow_table method

This method allows to create shadow table by existing table.

Two use cases:
a) create shadow table by table name
b) create shadow table from table instance

blueprint db-improve-archiving

Change-Id: Ib3a3797782b89a9a89baa60738edcabde7fe1299
Merge "Add sqlalchemy migration utils.check_shadow_table method"
Merge "Add sqlalchemy migration utils.create_shadow_table method"