Add pytest.oggm wrapper

This is a workaround for pytest-dev/pytest#1596
Without this, testing an installed version of oggm is impossible.

oggm/tests/__main__.py

@@ -0,0 +1,13 @@
+import os
+import sys
+
+HERE = os.path.dirname(__file__)
+
+
+def main():
+    import pytest
+    return pytest.main([HERE] + sys.argv[1:])
+
+
+if __name__ == "__main__":
+    sys.exit(main())

setup.cfg

@@ -51,3 +51,4 @@ console_scripts =
     oggm_prepro = oggm.cli.prepro_levels:main
     oggm_benchmark = oggm.cli.benchmark:main
     oggm_netrc_credentials = oggm.cli.netrc_credentials:cli
+    pytest.oggm = oggm.tests.__main__:main