[test] Update NAMD test

[rsarm]

Closes https://github.com/eth-cscs/reframe-tests/issues/35
Closes https://github.com/eth-cscs/reframe-tests/issues/33
Closes #540.

[rsarm]

@jenkins-cscs retry all

[vkarak]

This should not be merged. There are three issues related to NAMD, that I'd say should be addressed by a single PR. This PR must incorporate the change of #549 and invalidate that PR, and it must also address issue https://github.com/eth-cscs/reframe-tests/issues/33. I have also comments about the test itself, but I'll come back to them later.

[vkarak]

The test must be further refactored. Currently, they are a mixture of old and new syntax. This is how it should be done:

class NamdBaseCheck(rfm.RunOnlyRegressionTest):
    def __init__(self, version, variant):
        super().__init__()
        self.name = 'namd_%s_%s_check' % (version, variant)
        self.descr = 'NAMD check (%s, %s) % (version, variant)
        ...

@rfm.parameterized_test(['maint'], ['prod'])
class NamdGPUCheck(NamdBaseCheck):
    def __init__(self, variant):
        super().__init__('gpu', variant)
        ...

@rfm.parameterized_test(['maint'], ['prod'])
class NamdCPUCheck(NamdBaseCheck):
    def __init__(self, variant):
        super().__init__('cpu', variant)
        ...

You could also do everything in a single class that you instantiate four times. This is up to you.

[rsarm]

@jenkins-cscs retry daint