minor changes to prevent warning / errors

- make sure empty string test is made against a string
- removed an escape character that awk reports as ignored
- ignore errors when removing left-over intermediary .jtl files (or we
should test if they still exist before rm'ing them)
debug mode, working directory, additional logs

add: debutg mode (keep intermediary results and work files)
add: work directory for each project
add: jmeter execution log collection (may be big but can be useful to
have client side exceptions)