Make dotest.sh more dynamic

[bvdwiel]

The test runner is at present entirely hard-coded to perform a test the way I do them at work:

• Ramp up the concurrency level from 10 to 60 in steps of 10
• Run for 10 minutes at each concurrency level

Test runs should be configurable for at least the following:

• Concurrency level to start at
• Step-size for concurrency increment
• Concurrency level to stop at
• Test duration for each concurrency level

[bvdwiel]

Done, just not happy about it because it's not configurable when running loadtest.sh.. so not closing yet.

[bvdwiel]

Fudged it all into a config file.