dynamic_dns_lambda_client.sh: Various improvements
dynamic_dns_lambda_client.sh: Various improvements

Signed-off-by: Andrei Gherzan <8dc7c09356db0b1762fb140617d7375c0a5a4131@resin.io>

awslabs/route53-dynamic-dns-with-lambda,awslabs/route53-dynamic-dns-with-lambda