Fix Python binding tests

[DStrelak]

We have recovered some long-forgotten tests of the python binding.
See #688
It seems that meanwhile we have changed the test data, so some tests were failing due to missing test data.
Try to recover / redesign the tests that were commented out:

• PythonBindingTest.test_Image_add
• PythonBindingTest.test_Image_minus
• PythonBindingTest.test_Image_project
• PythonBindingTest.test_Image_projectFourier
• PythonBindingTest.test_Image_read
• PythonBindingTest.test_Image_readApplyGeo
• PythonBindingTest.test_Metadata_getValue
• PythonBindingTest.test_Metadata_importObjects
• PythonBindingTest.test_Metadata_iter
• PythonBindingTest.test_Metadata_existsBlockInMetaDataFile
• PythonBindingTest.test_Metadata_read
• PythonBindingTest.test_Metadata_read_with_labels
• PythonBindingTest.test_Metadata_setColumnFormat
• PythonBindingTest.test_Metadata_setValue
• PythonBindingTest.test_Image_multiplyDivide - division does not work (see TODO)

The Metadata* tests might need a following test.xmd file (as mentioned in one of the comments in the file)

        '''This test should produce the following metadata, which is the same of 'test.xmd'
        data_
        loop_
         _image
         _CTFModel
         _CTF_Defocus_U
         _count
         _classificationData
         _ref3d
         000001@pythoninterface/proj_ctf_1.stk  CTFs/10.ctfparam  -100.000000         10 ' 1.000000     2.000000     3.000000 '         -1
         000002@pythoninterface/proj_ctf_1.stk  CTFs/10.ctfparam   200.000000         20 ' 1.000000     4.000000     9.000000 '          2
         000003@pythoninterface/proj_ctf_1.stk  CTFs/10.ctfparam  -300.000000         30 ' 1.000000     8.000000    27.000000 '         -3
        '''

Also, it seems that skipped tests are not shown. That should be fixed as it's misleading.