Clarify USER instruction documentation

Reuse WORKDIR wording to specify that the USER instructions affect the
following RUN, CMD, and ENTRYPOINT instructions.

Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>
Fix help text being incorrect with multiple args

E.g. "docker foobar run" would have printed "Command not found:
foobar" and printed the help text for "run". It should instead
print the root help message for docker.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Fix deadlock in ps exited filter

Fixes #8909

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>
Merge pull request #8929 from LK4D4/fix_filter_hang

Fix deadlock in ps exited filter
Merge pull request #8927 from bfirsh/dont-pass-args-to-help-when-command-doesnt-exist

Fix help text being incorrect with multiple args
Merge pull request #8907 from icecrime/clarify_user_instruction_doc

Clarify USER instruction documentation