SshTransport.gettree: allow non-existing nested target directories

[sphuber]

Fixes #4174

The gettree method would raise an OSError for the SshTransport if
the target local path contains intermediate subdirectories that are not
created beforehand. The same would work without problem for the
LocalTransport plugin. It makes sense to just create non-existing
directories along the way, so the os.mkdir command that was used
originally to create the target directory is replaced with the method
os.makedirs setting exists_ok=True.

[sphuber]

It is interesting that this went unnoticed. This came up during development of the aiida-quantumespresso-hp plugin, but I definitely would have thought that retrieving a folder to a nested local folder would not be such an exotic use case.

[codecov]

Codecov Report

Merging #4175 into develop will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #4175      +/-   ##
===========================================
- Coverage    78.89%   78.88%   -0.00%     
===========================================
  Files          467      467              
  Lines        34470    34470              
===========================================
- Hits         27191    27189       -2     
- Misses        7279     7281       +2     

Flag	Coverage Δ
#django	70.81% <100.00%> (ø)
#sqlalchemy	71.68% <100.00%> (-<0.01%)	⬇️

Impacted Files	Coverage Δ
aiida/transports/plugins/ssh.py	76.39% <100.00%> (ø)
aiida/engine/daemon/client.py	72.58% <0.00%> (-1.14%)	⬇️

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[ramirezfranciscof]

Good to go for me!

[ramirezfranciscof]

The only thing is that when I try to test the transport locally I keep running into problems. This is clearly my issue because the test pass on the CI and this also happened before when I was trying to do some modifications in the transport, but do you have any idea of what may it be? I think all of the tests get the same error:

paramiko.ssh_exception.NoValidConnectionsError: [Errno None] Unable to connect to port 22 on 127.0.0.1 or ::1

(test the transport locally = pytest run the test/transports/test_all_plugins.py locally)

[sphuber]

Seems like you might have a problem with the configuration of the openssh-server on your localhost. We are testing the SshTransport by connecting to localhost over ssh. You may have blocked the port 22 or maybe the server is not even running?

[sphuber]

Thanks for the review. Let's wait with merging until @giovannipizzi has had a look to make sure I am not patching a problem that has its origin elsewhere