[feat] Additional Spack build system options

[jack-morrison]

1. Add support for user-defined spack env create options

ReFrame, unless targeting a user-specified existing Spack environment, automatically passes the -d rfm_spack_env option to create an ephemeral environment. This is a small addition that allows users to define extra spack env create options (link to Spack docs for list of options).

With the changes proposed here, a user could define the following:

self.build_system.env_create_opts = ["--without-view"]

which produces following in the build job script:

spack env create -d rfm_spack_env --without-view

While technically this allows for any spack env create options, my motivation for this feature is use of --without-view. ReFrame's use of temporary Spack environments leaves little use for a filesystem view, and disabling it can reduce the possibility of spack load-time spec collisions.

2. Add support for inserting commands between Spack environment creation and environment installation

Under certain circumstances it may be necessary to run complex custom commands to prepare a Spack environment. This needs to happen post-creation, but pre-installation. This capability is added to the Spack build system via build_system.preinstall_cmds.

[jenkins-cscs]

Can I test this patch?

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (fa813d0) 86.98% compared to head (b7bf09a) 86.99%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2919   +/-   ##
========================================
  Coverage    86.98%   86.99%           
========================================
  Files           60       60           
  Lines        11627    11635    +8     
========================================
+ Hits         10114    10122    +8     
  Misses        1513     1513           

Impacted Files	Coverage Δ
reframe/core/buildsystems.py	96.27% <100.00%> (+0.08%)	⬆️

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[victorusu]

lgtm