couchbase: allow to customize the IndexStorageMode

[daschl]

This changeset allows to customize the index storage mode, which has been previously been defaulting to memory optimized. By allowing for customization pre startup, it achieves:

• compatibility with the community edition by allowing the user to set it to forestdb
• setting it to plasma which is another engine available in the enterprise edition

The default still is memory optimized, since it seems to be the best option in a testing/CI environment.

(relates to #3419)

[daschl]

Updated - is this good to go @aaronjwhiteside @bsideup ?

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

[aaronjwhiteside]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

keep alive!

[daschl]

@rnorth @bsideup can we merge this please?

[eddumelendez]

Hi @daschl! I am looking into the PR and looks like nowadays it is possible to use the couchbase docker image with forestdb because of this. However, this PR allows to use an additional mode PLASMA. If I get it right, memory_optimized and plasma are used in enterprise edition and forestdb only in community edition, right?