Deleting incremental backup metadata after restore

The incremental backup was previously being unpacked in
/var/lib/mysql. This was mistakenly causing mysql to present this
folder as a database schema.

Change-Id: I22d5dbcf1e811d59bf19404ca884a09f87ca6bd0
Closes-Bug: #1334059
Merge "Deleting incremental backup metadata after restore"