Silence external commands output by default

[iyehuda]

Is your feature request related to a problem? Please describe.
Every command that bring executes (e.g. docker pull) may be verbose and print confusing text.

Describe the solution you'd like
It will be better to:

1. Print custom messages by default (e.g. "Pulling image...", "Saving images to /tmp/images.tar", etc.)
2. Have an option to turn on external commands output with --verbose global flag
3. Have an option to turn off outputs with --quite flag

Describe alternatives you've considered
One can run bring ... &> /dev/null but it is not that comfortable.

Additional context
It may be a good opportunity to implement a logger for the mission.