Without credentials should have non-zero exit status

[iain]

Currently if you run the command, and you haven't set up AWS credentials properly, it won't execute your command, but have a zero exit status, suggesting that everything went okay. Wouldn't it make more sense if it exited with a non-zero status?

Example:

bash-4.4# env-aws-params --prefix /foobar /bin/ls && echo $?
ERROR: NoCredentialProviders: no valid providers in chain. Deprecated.
	For verbose messaging see aws.Config.CredentialsChainVerboseErrors
0

[gmr]

That does make sense

[dave-shawley]

This should be fixed by #18