Fix configuration behavior in Ruby SDK.

Fix configuration behavior in Ruby SDK.

API_VERSION is not configuration: it indicates how a client program
expects the API server to behave. (No environment variable or config
file should try to override that.)

Do not invoke insecure behavior unless API_HOST_INSECURE is "1",
"true", or "yes".

If API_HOST and API_TOKEN environment variables are set, do not bother
reading the configuration file at all.

Strip spaces so "API_TOKEN = foo" works in the configuration file.