`-l` option lists multiple times the same checks

[vkarak]

$ ./bin/reframe -C config/cscs.py -c cscs-checks/libraries/petsc/petsc_helloworld.py -l
./bin/reframe: could not initialize the graylog handler; ignoring ...
[ReFrame Setup]
  version:           3.3-dev2 (rev: f75934ac)
  command:           './bin/reframe -C config/cscs.py -c cscs-checks/libraries/petsc/petsc_helloworld.py -l'
  launched by:       karakasv@dom101
  working directory: '/users/karakasv/Devel/reframe'
  settings file:     'config/cscs.py'
  check search path: (R) '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py'
  stage directory:   '/users/karakasv/Devel/reframe/stage'
  output directory:  '/users/karakasv/Devel/reframe/output'

[List of matched checks]
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_static (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
- PetscPoisson2DCheck_dynamic (found in '/users/karakasv/Devel/reframe/cscs-checks/libraries/petsc/petsc_helloworld.py')
Found 12 check(s)
Log file(s) saved in: '/users/karakasv/Devel/reframe/reframe.log', '/users/karakasv/Devel/reframe/reframe.out'

The problem seems to be coming from here:

https://github.com/eth-cscs/reframe/blob/f75934acf5239394ce637feb665032f31146a7fb/reframe/frontend/cli.py#L115

The problem is that RegressionTest objects are not hashed properly.