Warnings in tests

[bsolino]

The current tests are giving 6 avoidable/expected warnings:

https://travis-ci.org/github/NLeSC/mcfly/jobs/713626858#L2807

tests/test_find_architecture.py::FindArchitectureBasicSuite::test_find_best_architecture

tests/test_integration.py::IntegrationSuite::test_integration

tests/test_storage.py::StorageSuite::test_loadmodel

tests/test_storage.py::StorageSuite::test_savemodel

tests/test_storage.py::StorageSuite::test_savemodel_keras

  /home/travis/miniconda/envs/test-environment/lib/python3.7/site-packages/mcfly/modelgen.py:88: UserWarning: Specified number_of_models is smaller than the given number of model types.

    warnings.warn("Specified number_of_models is smaller than the given number of model types.")

tests/test_integration.py::IntegrationSuite::test_integration

  /home/travis/miniconda/envs/test-environment/lib/python3.7/site-packages/mcfly/find_architecture.py:240: UserWarning: Argument 'metric' is deprecated and will be ignored.

    warnings.warn("Argument 'metric' is deprecated and will be ignored.")

[bsolino]

Pull request #265 solved trivial warnings, one non trivial warning is missing: https://travis-ci.org/github/NLeSC/mcfly/jobs/713646901#L2807
It is related to issue #266