Adds FDB Tenants

[JesseStimpson]

Hi!

This commit adds support for FDB Tenants to erlfdb, and I wanted to offer it for your consideration.

I used the source for the official FDB Python and Java clients as reference.

Further guidance needed

There are some decisions that will probably raise an eyebrow. They are:

• Updated FDB_API_VERSION and api_version to 730, from 620.
• Changed unit test get_empty_test to use Tenants.

API version

Tenant support exists in some version after 620, though I did not pinpoint it precisely. Presumably this would be a breaking change for anyone using a cluster with <= 620. Guidance is appreciated here.

Empty Unit Test

I almost got myself into a pickle by running unit tests using a real cluster file. Perhaps I should have known better, but I didn't expect the unit tests to run a full clear_range. (Especially given that the unit tests are set to run with a simple make command). Luckily, the cluster I used only contained dev data, so no harm done. However, this seemed like an opportunity to use tenants to conduct the test in a safe manner.

[nickva]

Thank you for your PR, @JesseStimpson!

The implementation looks reasonable. For the FDB_API_VERSION version, from what I remember, we usually target some minimal supported version explicitly. That is why we had a hard-coded version there.

Unfortunately, I don't have a current working FDB setup to validate the PR in depth. If you're willing, feel free to fork and maintain the repo. I don't think anyone has been updating or looking at this repo besides me in a while.

I almost got myself into a pickle by running unit tests using a real cluster file. Perhaps I should have known better, but I didn't expect the unit tests to run a full clear_range.

Oof. Sorry about that. Yeah, the tests usually assume they have full rein on the cluster and just wipe it out. Perhaps the new tenants feature could help with that.

[JesseStimpson]

Thanks @nickva ! I've moved this work over to foundationdb-beam#1