Since current getting schema for CapnProto doesn't use cache, the
integration test was for the future if someone add cache.
Also, I was curious how schema cache affects performance and I compared reading binary files
with Protobuf (I guess it works the same for CapnProto).
```
for i in {1..1000}; do clickhouse-client -q \
"select * from test.simple format Protobuf settings format_schema='/format_schemas/simple:KeyValuePair'" > simple-protobuf${i}.bin; done
clickhouse-client --time -q "select * from file('simple-protobuf{1..999}.bin', 'Protobuf') format Null settings format_schema = 'simple:KeyValuePair'"
```
Protobuf with cache and without works with approximately the same
time.
Before it was impossible to update Protobuf schema without server
restart. With this commit, it is enough to send query `SYSTEM DROP
SCHEMA FORMAT CACHE [FOR Protobuf]`.
This PR formats all the `*.py` files found under the `tests/integration`
folder. It also reorders the imports and cleans up a bunch of unused
imports.
The formatting also takes care of other things like wrapping lines and
fixing spaces and indents such that the tests look more readable.
