Users can upload, delete and retrieve list of their public keys.
User can upload test result with any public keys without any connection
with uploading public keys in Refstack. It means that you can upload
signed test results and upload public key later. Also, it means that
deleting public key doesn't mean deleting results signed with this key.
Change-Id: Idc418c4c90221740eef04fcf498d7071a4446b9c
217cadd608