Fix --test for ceylon test tool.

when multiple elements are specified for --test,
--test should be repeated multiple times like this:
--test='function com.acme.foo::bar' --test='function com.acme.foo::baz'
 instead of having only one --test with ',' separated elements like this:
--test='function com.acme.foo::bar','function com.acme.foo::baz'