Timeout and basic error handling in reading a remote file

[JaeseungYeom]

Currently, a consumer will wait indefinitely if a file does not exist. A timeout controlled via environment variable might be useful. In addition, if there is an error while reading a file on the producer side, the error should be passed to the consumer.

[JaeseungYeom]

The timeout here is for KVS. This is different from issue #31

[JaeseungYeom]

PR #93 addresses a part of the plan, which is to send the return value of read() from module to client.