Improve jupyter launching (Jupyter Lab + enhanced alternate PORT)

[y2kbugger]

What is the purpose of this PR?

• Launch Jupyter as Jupyter Lab instead of Jupyter Notebook
• Enhance start_docker.sh to pass the first available port to jupyter so that "remapped port" warning is no longer required.
• Enhance available port detection to be more reliable
• Add execute to start_docker.sh to allow running directly, updated readme to match.

How did you implement your changes

I've touched start_docker.sh and Dockerfile.
For details, see commit history as I have broken up commits to tell story clearly.

Remaining issues

None

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[y2kbugger]

@ngreenwald Figured we could merge this into master prior to finalizing the metacluster GUI.

[ngreenwald]

Overall looks good! Is there a code cleanliness reason that having the script be executable is preferable to running bash scriptname? Or just a personal preference?

[y2kbugger]

Overall looks good! Is there a code cleanliness reason that having the script be executable is preferable to running bash scriptname? Or just a personal preference?

I'd say it follows "least astonishment" since it allows both bash ./script.sh and ./script.shand different people might be used to one or another.
Marking as executable also made sense since the script already included a the "hash-bang" (#!), which does nothing if not ran directly.

start_docker.sh

#!/bin/bash
...

[y2kbugger]

I did just push a small change, to use the slightly more portable #!/usr/bin/env bash ipo #!/bin/bash

https://stackoverflow.com/questions/10376206/what-is-the-preferred-bash-shebang

[ngreenwald]

Got it, that all makes sense.