Refactor Bzip2 tests

Motivation:

Complicated code of Bzip2 tests with some unnecessary actions.

Modifications:

- Reduce size of `BYTES_LARGE` array of random test data for Bzip2  tests.
- Removed unnecessary creations of `EmbeddedChannel` instances in Bzip2 tests.
- Simplified tests in `Bzip2DecoderTest` which expect exception.
- Removed unnecessary `testStreamInitialization()` from `Bzip2EncoderTest`.

Result:

Reduced time to test the 'codec' package by 7 percent, simplified code of Bzip2 tests.