[1.3] Support injecting failpoints to mimic syscall errors

[ahrtr]

We need to backport the following PRs to release-1.3:

• Support injecting failpoints to mimic syscall errors  #383
  • The PR was merged before we created release-1.3, so it's already included in release-1.3.
• Change error handling logic in db.close() #400
  • [1.3] Backport change to error handling logic #439
• Perform unmap when mlock fails or both meta pages corrupted #433
  • [1.3] Backport perform unmap when mlock fails or both meta pages corrupted #444

[jmhbnz]

Keen to pick this one up to keep learning more about how bbolt works. Have raised backport pr #439.

/assign @jmhbnz

Note: @ahrtr #383 was included as needing backport above but unless I am missing something it looks like this is already done?

[ahrtr]

Thanks @jmhbnz .

#383 was merged before we created release-1.3, so it's already included in release-1.3.

I suggest to backport #400 and #433 in two separate PRs.

[jmhbnz]

I suggest to backport #400 and #433 in two separate PRs.

No problem, first pr updated to just reflect the first task 👍🏻

[ahrtr]

All tasks done. Thanks @jmhbnz