CI: Attempt to test all scripts on merge to master

[Lestropie]

Adds a Dockerfile for building a container tailored for executing all script tests, including those with external neuroimaging software dependencies. An additional workflow is then intended to build and execute that container only for merges to master.

[Lestropie]

Note to self: Currently the CI will have to download & install the whole system, in addition to fixed versions of ANTs and FSL, for every CI test. An alternative would have to be a pre-built container based on an additional repository, which includes all of these contents: this repository would then simply specify this container in the Dockerfile recipe. The disadvantange would be that updates to other neuroimaging softwares would not immediately be imported; but this would simply require updating and rebuilding that template container.

[Lestropie]

  Step 10/16 : RUN wget -q http://fsl.fmrib.ox.ac.uk/fsldownloads/fslinstaller.py -O /fslinstaller.py     && chmod 775 /fslinstaller.py     && python2 /fslinstaller.py -d /opt/fsl -V 6.0.4 -q     && rm -f /fslinstaller.py     && ( which immv || ( rm -rf /opt/fsl/fslpython && /opt/fsl/etc/fslconf/fslpython_install.sh -f /opt/fsl || ( cat /tmp/fslpython*/fslpython_miniconda_installer.log && exit 1 ) ) )
   ---> Running in 40f6e1aec579
  [FAILED] Unable to unpack FSL - Unable to unpack FSL.
  The command '/bin/sh -c wget -q http://fsl.fmrib.ox.ac.uk/fsldownloads/fslinstaller.py -O /fslinstaller.py     && chmod 775 /fslinstaller.py     && python2 /fslinstaller.py -d /opt/fsl -V 6.0.4 -q     && rm -f /fslinstaller.py     && ( which immv || ( rm -rf /opt/fsl/fslpython && /opt/fsl/etc/fslconf/fslpython_install.sh -f /opt/fsl || ( cat /tmp/fslpython*/fslpython_miniconda_installer.log && exit 1 ) ) )' returned a non-zero code: 1
  ##[warning]Docker build failed with exit code 1, back off 8.871 seconds before retry.
  /usr/bin/docker build -t 3b3ac6:84564b29c60e43bfb8327824a5fd2027 -f "/home/runner/work/_actions/MRtrix3/script_test_action/master/Dockerfile" "/home/runner/work/_actions/MRtrix3/script_test_action/master"
  Sending build context to Docker daemon  8.704kB
  
  Error response from daemon: Error processing tar file(exit status 1): write /action.yml: no space left on device

:-/

[Lestropie]

Container grabs code, compiles and starts tests, but they get terminated after 6 hours.
So will need to pursue test data drastically reduced in spatial resolution to complete more quickly, and/or Daan's suggestion of replacing external software commands with dummies that dump pre-generated data; but given population_template is one of the culprits, reduction in spatial resolution is probably going to be needed regardless.

[Lestropie]

@maxpietsch: I've massively cut down on dwifslpreproc test run times trying to make CI tests with little to no multi-threading and 6 hour runtime feasible (and hopefully actually add more tests to verify all of its features). Ideally I'd like to cut down on population_template substantially too since that's the other primary culprit. There's a few things we could do e.g.:

• Reduce spatial resolution;

• Reduce the number of tests that are done comprehensively looking for regressions in output data; for those that only need to be run to verify completion given command-line options, we could cut number of stages / number of iterations within each stage.

Though CI is actually out of time before the tests even reach that point, so there needs to be further cuts elsewhere...