Fixing matplotlib libGL

[felipelm]

We had this problem running the pipeline:

2018-06-12 14:38:21,434 QuickLook ERROR : Failed to import Check_HDUs from desispec.qa.qa_quicklook. Error was 'libGL.so.1: cannot open shared object file: No such file or directory'
Traceback (most recent call last):
  File "/app/desispec/bin/desi_quicklook", line 7, in <module>
    quicklook.ql_main(quicklook.parse())
  File "/app/desispec/py/desispec/scripts/quicklook.py", line 117, in ql_main
    pipeline, convdict = quicklook.setup_pipeline(configdict)
  File "/app/desispec/py/desispec/quicklook/quicklook.py", line 555, in setup_pipeline
    if not qa.is_compatible(pa.get_output_type()):
AttributeError: 'NoneType' object has no attribute 'is_compatible'

This PR fixes it. Please let me know your thoughts I'm not sure if this is the best solution.

[Srheft]

@felipelm :
see line 52-54 in py/desispec/scripts/quicklook.py
running ql_TagUpdate_0.21.0 does not return such error.

qlf could run that tag that is pretty much the same as 0.21.0 with few internal changes [nothing abiout the outputs have changed].

[felipelm]

Tried running ql_TagUpdates_0.21.0 and got another error:

2018-06-12 17:25:13,449 QLConfig WARNING : WARNING, can't open template file /app/spectro/redux/exposures/20191017/00003900/ql-mergedQA-z2-00003900.json
2018-06-12 17:25:15,086 QLConfig INFO : Checking if all the necessary files exist.
2018-06-12 17:25:15,087 QLConfig INFO : File check: Okay: /app/spectro/data/20180619/desi-00000021.fits.fz
2018-06-12 17:25:15,088 QLConfig INFO : File check: Okay: /app/spectro/data/20180619/fibermap-00000021.fits
File does not exist: /app/spectro/redux/exposures/20180619/00000002/fiberflat-z2-00000002.fits

We suspect that the calibration files changed so we will use this PR branch and wait for the next release.

[Srheft]

@felipelm
the error is not algorithmic:
File does not exist: /app/spectro/redux/exposures/20180619/00000002/fiberflat-z2-00000002.fit

As I mentioned many times in emails, one has to edit the configuration files. They are uploaded on github in a general form because we don't know which night qlf would try them on. So when you decide which flat and arc exposure you are trying, then you have to edit the configuration file and put exposure id if the arc and flat in their respected places.

[felipelm]

Ok we will make sure we use the correct one. Matplotlib error is fixed on ql_TagUpdates_0.21.0 so we will use it.

Thanks @Srheft

[Srheft]

Great! ql_TagUpdate_0.21.0 should also remove any possible Cholesky decomposition failure.