Requests made by client with key=invalid argument

[david4096]

ga4gh/ga4gh-server#601

This command

python client_dev.py -O variants-search http://localhost:8000 --variantSetId ZGF0YXNldDE6MWtnLXBoYXNlMQ==

results in a request to

/variants/search?key=invalid

If the key=invalid part is not necessary (which I suspect it is not), we should not make requests with that argument.