Pass through return values from inside Docker to the Go wrapper

[vikrum]

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If a call to Introspector fails or the query returns a failure, the Go wrapper should return a non-zero return value to the calling shell.

🤖 17:08:30 anglegrinder:introspector$ ./introspector asdfasdf
Usage: introspector.py [OPTIONS] COMMAND [ARGS]...
Try 'introspector.py --help' for help.

Error: No such command 'asdfasdf'.

🤖 17:08:40 anglegrinder:introspector$ echo $?
0

[vikrum]

https://github.com/goldfiglabs/introspector/commit/802d66be48ff9cdf30a118c343cbbcbe830d3205