QtcProcess: pass arguments only once to child process

When not using the ctrlc stub, then the whole arguments string was
passed to QProcess::start as one argument, prefixed to the actual
arguments.

Task-number: QTCREATORBUG-11514

Change-Id: I8111749b5c2f0a0abbfa3e9f8441bb5cdcfe0531
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: hjk <hjk121@nokiamail.com>