On the container exec command, return the same exit code of
the command being executed in the container. This would be
useful for users to retrieve the exit code as they did in
Docker CLI.
Change-Id: I2aa0b4d9e7994a125f54e93d36efc854db66fe25
Depends-On: I20cc48da20bdc3784ec8fce4e38a98baf388a0ca
Closes-Bug: #1645044