Improve error handling

[mfgumban]

Scenario:

• ML server is up but currently "busy" (ingesting large data)
• User hits Koop with a query
• Koop tries to contact ML but will get an error
• Koop will exit because it wasn't able to properly handle the error response

Sample Error:

koop          | /app/node_modules/marklogic/node_modules/bluebird/js/release/async.js:61
koop          |         fn = function () { throw arg; };
koop          |                            ^
koop          |
koop          | TypeError: Cannot read property 'errorResponse' of undefined
koop          |     at /app/src/koop/query.js:23:33

Code in line 23: reject(new Error(error.body.errorResponse.message)); needs to be modified to inspect error.body first, then make an appropriate action.

[rjrudin]

OBE, the line of code this refers to no longer exists.