Bugfix for Jmeter when all transactions fail

Fixes
* Errors when the failure rate for a transaction is 100%
* Fixes bug where failures of one transaction was assumed to imply failure in other transactions
* Sanitize Transaction Names containing "/" and "?" which led to exceptions and/or failed client charting
Agreed. But even for quick fix, lets change '/' to space or '_'. 

Pull request LGTM otherwise