Error state if knex can't reach db server

[knownasilya]

GET /dashboard/ 500 10.982 ms - 569
Error: connect ENETUNREACH
    at errnoException (net.js:904:11)
    at connect (net.js:766:19)
    at net.js:845:9
[TypeError: Cannot read property '__cid' of undefined]
TypeError: Cannot read property '__cid' of undefined
    at Runner_PG.<anonymous> (/Users/knownasilya/workspace/myproject/node_modules/knex/lib/runner.js:117:30)
    at tryCatch1 (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/util.js:63:19)
    at Runner_PG.Promise$_method [as query] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/promise.js:267:25)
    at Runner_PG.<anonymous> (/Users/knownasilya/workspace/myproject/node_modules/knex/lib/runner.js:44:19)
    at tryCatch1 (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/util.js:63:19)
    at Promise$_callHandler [as _callHandler] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/promise.js:695:13)
    at Promise$_settlePromiseFromHandler [as _settlePromiseFromHandler] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/promise.js:711:18)
    at Promise$_settlePromiseAt [as _settlePromiseAt] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/promise.js:868:14)
    at Promise$_settlePromises [as _settlePromises] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/promise.js:1006:14)
    at Async$_consumeFunctionBuffer [as _consumeFunctionBuffer] (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/bluebird/js/main/async.js:74:12)


GET /dashboard/ 500 32.005 ms - -

/Users/knownasilya/workspace/myproject/node_modules/knex/lib/pool.js:45
      connection.end();
                 ^
TypeError: Cannot call method 'end' of undefined
    at Object.destroy [as destroyHandler] (/Users/knownasilya/workspace/myproject/node_modules/knex/lib/pool.js:45:18)
    at Object.Pool.destroy (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/generic-pool-redux/pool.js:238:12)
    at Object.Pool.removeIdle (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/generic-pool-redux/pool.js:261:14)
    at null.<anonymous> (/Users/knownasilya/workspace/myproject/node_modules/knex/node_modules/generic-pool-redux/pool.js:279:27)

Three errors:

• connect ENETUNREACH
• Cannot read property '__cid' of undefined
• Cannot call method 'end' of undefined

Seems like the connection should be checked if it was ever instantiated before destroying, plus the check for the query object being there. Better error messages are needed here.

[bendrucker]

Same idea as #545. It should be possible with certain errors to say "the pool just failed to get a connection and the error suggests it will never succeed."

[bendrucker]

Sorry, #595