Add datastore tests

[magik6k]

Datastores (mostly badger for now) should get some more testing, this can be done in couple of ways:

• Sharness test running the a test set for a number of datastore configurations
  • Need to get a good set of tests operating on datastore to test well
  • CI won't take much longer to run
• Running some sharness tests multiple times for different configs
  • Tests will take more time to run
  • Should stress the datastores rather well
• Running all sharness tests with different configs
  • Probably overkill
  • Tests will take forever to run

[whyrusleeping]

Some things for the list of things to test:

• garbage collection actually frees up space
• reasonable errors when running out of disk space (no corruption)
• putting and deleting the same value back and forth many times doesnt cause problems

[schomatis]

I'm assigning (temporarily) this issue to myself while I prepare some tests for the Badger implementation, you could guide me to structure those tests in a way that they may be re-utilized in the future for the generic datastore interface. (Sometimes that won't be possible as some tests need to interact directly with badger-specific settings.)

[schomatis]

@magik6k Do you know of any sharness test I could use as a base for the datastore tests?

[magik6k]

For some relevant tests I'd start with 40-add-and-cat, 45-ls, 50-block, 53-dag, 80-repo and 81-repo-gc-auto.

Optimally we'd be able to tell sharness/make to re-run some tests with different datastore/profile.