Esmvaltool: Use Debian container without Conda in CircleCI

[nielsdrost]

Conda is causing a lot of noise testing ESMValTool as packages are very much as moving target.

We should build a Debian container using only Debian and Pypi packages. We can then use this to make the CircleCI testing faster and/or more stable. It also serves as a working example of how to install ESMValTool on a Debian/Ubuntu machine.

[bouweandela]

@zklaus I assigned you because you offered to help out with this. Please let me know if I can support you in any way.

[zklaus]

I'll have a look.

[ipelupessy]

I have been building and installing the ESMValTool stack on an opensuse (tumbleweed) machine
in a virtualenv environment.

just a few notes that can be helpful:

• I noticed that pip installing binary wheels caused nasty problems/ collisions with system installed libraries, so I had to pip install --no-binary the following: Fiona, netCDF4
• I have installed and build the following libraries/ python packages 'by hand':
  cartopy, pyke (this is a very old apparently static package), stratify, gdal (system one was too new (3.0.1), udunits, ncl (non standard configuration, it also has many optional dependencies - I took a minimum set with a risk ofcourse...), esmf
• in the end I pip -e installed: ESMValCore, ESMValTool and iris

if I remember anything else, will add it here...