Feature/cache option ignore errors

[aniketawati]

Description of change

In case of cache errors like network failure, redis out of memory etc, default behaviour is to return that error to the caller.
But there are some cases where cache is only there to minimize database calls and its failure can be tolerated.
Issue #926 has been pending for this purpose.

This change introduces cacheoption - ignoreErrors and based on its value decides to throw the cache error or not.

Closes #926

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change
• Documentation has been updated to reflect this change
• The new commits follow conventions explained in CONTRIBUTING.md

[AlexMesser]

thank you for contribution!

[jason-hwang]

@aniketawati
First of all, thank you for your contribution.
and also, I have a question about this change.

Problem

In my expectation, my node-js server will not be broken If redis server is shutdown
when the ignoreErrors option is applied.

But I've faced the crash like this

Error: Redis connection to localhost:6379 failed - connect ECONNREFUSED 127.0.0.1:6379
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1056:14)
error Command failed with exit code 1.

I know that is an abnormal case, but I assumed the redis server is broken by unpredictable scenarios.
Can you give more insight?