Consistency in batch file API

[tohojo]

Currently, multiple host names are separated by commas in the batch file, while multiple test parameters are separated with semi-colons (because the test parameters themselves can contain commas).

It would be good to harmonise this as it's a source of confusion; supporting semi-colons for separating hosts should be trivial, supporting commas for test parameters would require implementing proper quoting (which is probably a good idea to do anyway).