Sailor should be more tolerant of invalid LOG_LEVEL values

[jhorbulyk]

Consider the following cases:

• A user enters IFNO as the LOG_LEVEL env var for a component
• A user enters INFO (with lead space) as the LOG_LEVEL env var for a component
• A user enters INFO, DEBUG as the LOG_LEVEL env var for a component (doesn't logging understand heirarchy)

Results in the following exception being thrown on virtually any action involving the component:

throw new Error(format('unknown level name: "%s"', nameOrNum));
(no message)
at resolveLevel (/home/apprunner/node_modules/elasticio-sailor-nodejs/node_modules/bunyan/lib/bunyan.js:293:19)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
at Module.load (internal/modules/cjs/loader.js:928:32)
at Function.Module._load (internal/modules/cjs/loader.js:769:14)
/home/apprunner/node_modules/elasticio-sailor-nodejs/node_modules/bunyan/lib/bunyan.js:293
at Logger.addStream (/home/apprunner/node_modules/elasticio-sailor-nodejs/node_modules/bunyan/lib/bunyan.js:570:19)
at new Logger (/home/apprunner/node_modules/elasticio-sailor-nodejs/node_modules/bunyan/lib/bunyan.js:490:18)
at Function.createLogger (/home/apprunner/node_modules/elasticio-sailor-nodejs/node_modules/bunyan/lib/bunyan.js:1618:12)
at Object.<anonymous> (/home/apprunner/node_modules/elasticio-sailor-nodejs/lib/logging.js:36:20)
at Module.require (internal/modules/cjs/loader.js:952:19)
^
Error: unknown level name: "IFNO"
at Module._compile (internal/modules/cjs/loader.js:1063:30)

Ideally sailor should be more resillient and log an error while falling back to the defaults so that things don't catastrophically break on minor configuration errors.