Docker client fixes (#2419)
* force system COG_DOCKER_SDK_CLIENT through tox
* set contexts on frontend + bk session
* add timeout to predictor healthcheck request
* Ensure ports from cfg and image EXPOSE
* handle missing device driver error
* handle interactive but non-piped stdin
* add dockerfile:1 syntax to frontend args
* handle context path relative to working dir
* remove debug prints messing up test output
* formatting fix
* simpler attach stream checks
* logic improvements to attach & tty edge cases, tests
* unrelated `go mod tidy` change
* handle interactive TTY streams (eg running /bin/bash)
* add test for running /bin/bash w/ interactive tty
