Add SSH tunnel support

[sweenu]

Closes #459

Description

This PR adds support for creating SSH tunnels thanks to the sshtunnel package.

If you want this PR to be merged, then I'll write some tests. Let me know :)

I know it might increase the support load, but I think it's worth it. Right now, basically everyone that need tunnels are doing their own wonky scripts to create tunnels and shut them down automatically after pgcli exits (I have one myself). It is work and time that can be avoided by having a central way of doing it. It's also very nice to be able to give pgcli the DB uri as if you were directly connecting to it and not have to change it to match your local bind of the SSH tunnel.

For the future:

• It'd be nice to be able to pass extra arguments to sshtunnel. But this should already cover most usecases, special config can just go in the ssh conf.
• To have a section in the config that will allow matching hostnames and automatically create a tunnel for those.

Checklist

• I've added this contribution to the changelog.rst.
• I've added my name to the AUTHORS file (or it's already there).

• I installed pre-commit hooks (pip install pre-commit && pre-commit install), and ran black on my code.
• Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)

[j-bennet]

I like this! Yes, it would be very nice to give users a built-in way to tunnel. Please go ahead with adding some tests.

This feature will need supporting documentation. Are you able to PR supporting docs into https://github.com/dbcli/pgcli.com? I suggest adding a dedicated page to describe ssh tunneling, and linking it in the docs.

[j-bennet]

Is sshtunnel difficult to install? Is there a reason we would not want to make it one of the default requirements?

[sweenu]

I made it optional because it is not a feature that most pgcli users will have the need for I think and it adds paramiko and sshtunnel as dependencies. But let me know if you prefer it wasn't optional.

[sweenu]

Glad that you'd accept it! I'll add tests and documentation.

[j-bennet]

@sweenu It seems that black check is failing in CI, take a look at that too.

[sweenu]

@j-bennet I have added tests and documentation. I also tried running black with python 3.6, but it changed nothing, so I wouldn't know where the pipeline error would be coming from if it fails again.

In the end, do you want to make it optional to install sshtunnel?

[j-bennet]

@sweenu Ok to leave sshtunnel as-is. Please take a look at those test failures in CI. Were you able to run tests successfully in your local environment, including behave tests?

[codecov-commenter]

Codecov Report

Merging #1301 (f2dfc3d) into master (3a95530) will increase coverage by 0.09%.
The diff coverage is 79.41%.

@@            Coverage Diff             @@
##           master    #1301      +/-   ##
==========================================
+ Coverage   83.80%   83.90%   +0.09%     
==========================================
  Files          21       21              
  Lines        2594     2709     +115     
==========================================
+ Hits         2174     2273      +99     
- Misses        420      436      +16     

Impacted Files	Coverage Δ
pgcli/completion_refresher.py	90.58% <50.00%> (-1.08%)	⬇️
pgcli/pgexecute.py	80.36% <74.72%> (-1.18%)	⬇️
pgcli/main.py	77.62% <85.13%> (+1.69%)	⬆️
pgcli/__init__.py	100.00% <100.00%> (ø)
pgcli/packages/parseutils/tables.py	97.67% <100.00%> (ø)
pgcli/pgcompleter.py	96.95% <100.00%> (ø)

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[j-bennet]

Tests are ok now. Going to merge the PR.