Added tests for EITMap in this commit.
1. Decided to test all FITS files in sunpy.data.test.EIT folder. Can change this back to just one FITS file if needed.
2. The _get_mpl_normalizer() function test makes EITMap tests different from HMI and AIA.
3. The colors.LogNorm object's creation has been tested, as well as its vmin and vmax properties.
4. All tests passed.