Fix typeError in lib/responseToError.js

[laurenzlong]

Description

Certain API calls (such as ones to cloudfunctions) return response bodies which are a JSON string. This change attempts to parse the string to retrieve error message and prevents type errors such as:

[2018-07-03T16:58:35.452Z] TypeError: Cannot create property 'error' on string '{
"error": {
"code": 503,
"message": "The service is currently unavailable.",
"status": "UNAVAILABLE",
"details": [
{
"@type": "type.googleapis.com/google.rpc.DebugInfo",
"detail": "[ORIGINAL ERROR] RPC::DEADLINE_EXCEEDED: "
}
]
}
}
'

Scenarios Tested

Sample Commands