Fix bandcount

[EmileSonneveld]

Summary:

• Some EmptyMultibandTiles where made with 0 bands. While there should be 'n' bands
• When asking EmptyMultibandTile for a list of bands, an empty array was returned, instead of a list of 'n' empty bands.

This caused problems when combining merge_cubes and aggregate_temporal. A test has been added that goes over many combinations of those, to filter out bugs.

[EmileSonneveld]

@bossie Jenkins gives errors like: Sentinel3PyramidFactoryTest.compareReferenceImage: /data/MTDA/TERRASCOPE_Sentinel3/COG/SY_2_VG1/S3A/2020/07/01/S3A_SY_2_VG1____20200701T120000_20200702T120000_20200707T122712_EUROPE____________LN2_O_NT_002/S3A_SY_2_VG1____20200701T120000_20200702T120000_20200707T122712_EUROPE____________LN2_O_NT_002.SEN3/S3A_SY_2_VG1____20200701T120000_20200702T120000_20200707T122712_EUROPE____________LN2_O_NT_002.SEN3/MIR.tif (No such file or directory)

But this test passes locally. Do you think it will work when merged on develop?

[bossie]

The majority of the jenkinsslaves have that mount but some don't so it's a matter of luck. I'll check with s-ops but don't let this keep you from merging into develop.