Set a sane default socket timeout

[danielmitterdorfer]

The current socket timeout is (mistakenly) 60.000 seconds (almost 17 hours). Presumably, this was meant in milliseconds but the value really is denoted in seconds (see client docs).

Therefore, we will reduce the default socket timeout in Rally to the originally intended value of 60 seconds (the ES client's default value is 10 seconds). This should be sufficient for normal use cases. If users wish to change that value they can provide e.g. --client-options="timeout:120" to raise this value to 120 seconds in this example.

Marking as "breaking" as the reduction to 1 minute may break existing benchmarks (although it's unlikely).