Allow ListShelves method to be called without API key (#701)
Allow ListShelves method to be called without API key (#701)

This simplifies our quickstart such that reader does not need to go
through an extra step to create an API key before calling this API.
hashems/Mobile-Cloud-Development-Projects,hashems/Mobile-Cloud-Development-Projects,GoogleCloudPlatform/python-docs-samples,canglade/NLP,GoogleCloudPlatform/python-docs-samples,hashems/Mobile-Cloud-Development-Projects,GoogleCloudPlatform/python-docs-samples,BrandonY/python-docs-samples,JavaRabbit/CS496_capstone,BrandonY/python-docs-samples,JavaRabbit/CS496_capstone,JavaRabbit/CS496_capstone,canglade/NLP,BrandonY/python-docs-samples,sharbison3/python-docs-samples,hashems/Mobile-Cloud-Development-Projects,canglade/NLP,canglade/NLP,JavaRabbit/CS496_capstone,sharbison3/python-docs-samples,sharbison3/python-docs-samples,sharbison3/python-docs-samples,BrandonY/python-docs-samples,GoogleCloudPlatform/python-docs-samples