Increase timeout for userland proxy starting

Fixes #8883

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>
test case for preserving env in exec session

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
Merge pull request #9174 from dqminh/docker-exec-env

Set correct env variables for `docker exec` commands
Merge pull request #9260 from LK4D4/increase_proxy_timeout

Increase timeout for userland proxy starting