Add fault injection mechanism

We need the ability to inject various forms of somewhat deterministic (As well as non-deterministic) faults into the test. This should be things like 'crashing' the server or xtrabackup process at various points to validate that the recovery and other tasks respond correctly. This should also be things such as injecting bad data into the server/source database befor and during backup as well as maligning data within the backup sets before and during restore to ensure proper error handling/reporting/recovery.