fix possible dm snapshot leaks

[chanwit]

There are some defers that won't be called if an error occurred by ActivateSnapshot.
It's gonna defer to DeactivateSnapshot anyway even if ActivateSnapshot return an error.

Signed-off-by: Chanwit Kaewkasi [email protected]

[chanwit]

Also kindly ping @luxas

[chanwit]

Also, could we have this for 0.6.x?

[chanwit]

kindly ping @stealthybox
I think we need to confirm this change a bit to make sure that it won't break the current behavior.

[stealthybox]

I was able to replicate these issues with the dm snapshots mentioned in #365 using a build on master.

This patch appears to fix it.
In general, this is an improvement in code quality.

Misplaced defer statements are a common source of error-handling issues.
Thanks for the thoughtful change 👍