eo:cloud_cover is never added to Assets

[pjhartzell]

When generating Items from XML files, eo:cloud_cover values are (supposed to be) drawn from two locations: The QAPERCENTNOTPRODUCEDCLOUD value in the PSAs element and the QAPercentCloudCover value(s) in the MeasuredParameter element. QAPERCENTNOTPRODUCEDCLOUD is assigned to the Item properties and the parameter/band QAPercentCloudCover values to the appropriate Item Asset.

There are a few bugs, though, that prevent the Asset eo values from ever being stored.

• Not stored because qa_percent_cloud_cover will always be empty/false:
  

  modis/src/stactools/modis/metadata.py

  Lines 151 to 163 in 2c15f8f

  	qa_percent_cloud_cover: Dict[str, int] = {}
  	measured_parameters = metadata.findall(
  	"MeasuredParameter/MeasuredParameterContainer"
  	)
  	for measured_parameter in measured_parameters:
  	name = measured_parameter.find_text_or_throw(
  	"ParameterName", missing_element("ParameterName")
  	).replace(" ", "_")
  	band_qa_percent_cloud_cover = measured_parameter.find_text(
  	"QAPercentCloudCover"
  	)
  	if qa_percent_cloud_cover:
  	qa_percent_cloud_cover[name] = int(band_qa_percent_cloud_cover)

• Assuming the above bug is fixed, assignment fails for assets not having an eo cloud_cover value (the key does not exist):
  

  modis/src/stactools/modis/builder.py

  Lines 292 to 293 in 2c15f8f

  	if self.metadata.qa_percent_cloud_cover:
  	asset_info.eo = {"cloud_cover": self.metadata.qa_percent_cloud_cover[key]}