Skip mosaic quads that a user does not have access to during downloading

[joferkington]

Permission for mosaic quad download often varies spatially for a given user. It's common for someone to have access to some quads within an AOI but not all. Currently, when a user tries to download quads they don't have access to the client raises an unexpected error:

ERROR - unexpected error in <planet.api.downloader._MosaicDownloadStage object at 0x10d87b240> Traceback (most recent call last):   File
"~/pl/planet-client-python/planet/api/downloader.py", line 159, in _process_task     self._do(self._doing)   File "/~/pl/planet-client-
python/planet/api/downloader.py", line 471, in _do     self._client.download_quad(task, writer)))   File "~/pl/planet-client-python/planet/api/client.py", line
363, in download_quad     download_url = quad['_links']['download'] KeyError: 'download'

This PR changes client.download_quad to raise a NoPermission error when that occurs and changes the planet mosaics download command (and associated downloader infrastructure) to skip mosaic quads that a user does not have permission for during downloading.

[sarasafavi]

thanks @joferkington !