Eliminate calling of `await()` in the docker library.

After making composing containerizer as a default containerizer in tests, some tests (e.g. `AgentAPITest.AttachContainerInputValidation`) started to hang due to a paused clocks and the use of clock-dependent method `await()` by the docker library.

Tests hang in `Docker::validateVersion()`, which is called from `Docker::create()` when an instance of docker containerizer is created.

A possible solution might be removing `DOCKER_VERSION_WAIT_TIMEOUT` or making both `Docker::validateVersion()` and `Docker::create()` asynchronous.