integration cli: add imageExists to docker utils

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
make TestRemoveContainerRunning handle signals

This lowers the test execution time by about 5 seconds.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
integcli: add & use pullImageIfNotExist for pulls

This speeds up the tag cli integration tests by about 20 seconds.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #6780 from unclejack/tweak_cli_integration_tests

Tweak cli integration tests