LCOGTingest should return a descriptive error when the date format is incorrect

[abostroem]

LCOGTingest.py and lscloop.py use different date formats (2020-01-01 vs 20201010). When the lscloop.py date format is used for LCOGTingest.py, it results in a non-descriptive error which is challenging to trace to the issue:

LCOGTingest.py -s 20200201 -e 20200331 -r reduced -t STANDARD --public -n L107
Traceback (most recent call last):
  File "/usr/local/bin/LCOGTingest.py", line 300, in <module>
    covers='POINT({} {})'.format(*args.coords) if args.coords else None)
  File "/usr/local/bin/LCOGTingest.py", line 37, in get_metadata
    frames = response['results']
KeyError: 'results'

LCOGTingest.py should either gracefully handle the different date formats or should recognize when the wrong format is used and let the user know