Status endpoint can specify the reason in case enclave setup fails

[prateekreddy]

Status endpoint currently provides IP address in case enclave starts up but doesn't really provide any reason in case enclave fails to start. It would help users if a reason was provided in case enclave fails, it can be due to enclave image url is not reachable or enclave image downloaded is corrupted, not enough CPUs, not enough memory and so on. This is especially useful when users are trying to figure an optimal resource allocation by manually setting memory.