Fix/implement single function deployment/invokation

[jikuja]

Handle missing non-existant function is serverless-hedge-plugin code.

AWS and Azure still will fail but error messages are more user friendly and more common than stacktraces from plugin code.

E.g. AWS plugin gives following error and stack when invoking locally with wrong function name:

ServerlessError: Function "calcFAILURE" doesn't exist in this Service
    at Service.getFunction (/usr/local/lib/node_modules/serverless/lib/classes/Service.js:195:11)
    at AwsInvokeLocal.extendedValidate (/usr/local/lib/node_modules/serverless/lib/plugins/aws/invokeLocal/index.js:50:56)
From previous event:
    at Object.invoke:local:invoke [as hook] (/usr/local/lib/node_modules/serverless/lib/plugins/aws/invokeLocal/index.js:24:10)
    at BbPromise.reduce (/usr/local/lib/node_modules/serverless/lib/classes/PluginManager.js:366:55)
From previous event:
    at PluginManager.invoke (/usr/local/lib/node_modules/serverless/lib/classes/PluginManager.js:366:22)
    at PluginManager.run (/usr/local/lib/node_modules/serverless/lib/classes/PluginManager.js:397:17)
    at variables.populateService.then (/usr/local/lib/node_modules/serverless/lib/Serverless.js:104:33)
    at runCallback (timers.js:773:18)
    at tryOnImmediate (timers.js:734:5)
    at processImmediate [as _immediateCallback] (timers.js:711:5)
From previous event:
    at Serverless.run (/usr/local/lib/node_modules/serverless/lib/Serverless.js:91:74)
    at serverless.init.then (/usr/local/lib/node_modules/serverless/bin/serverless:42:50)
    at <anonymous>

[jikuja]

Implemented and tested

• [X] AWS deploy function
• [X] AWS invoke local
• [ ] Azure deploy function
• [ ] Azure invoke local

Tested/fixed bad function name arguments

• [X] AWS deploy function

• [X] AWS invoke local

• [ ] Azure deploy function

• [ ] Azure invoke local

• AWS fixed with 2d14d9a5c1206c72c2d82ffce44921a513f5d75f

[jikuja]

Serverless plugin not in scope for Hedge anymore.