qemu: fix domain id after domainCreateWithFlags()
    
    Ever since virDomainCreateWithFlags() was introduced by de3aadaa
    [drivers: add virDomainCreateWithFlags if virDomainCreate exists], the
    domain ID retrieved with virDomainGetID() was incorrect for several
    drivers after virDomainCreateWithFlags() was called. The API consumer
    had to look up the domain anew to retrieve the correct ID.
    
    For the ESX driver, this was fixed in 6139b274 [esx: Update ID after
    starting a domain]. For the openvz driver, it was fixed in fd81a097
    [openvzDomainCreateWithFlags: set domain id to the correct value]. The
    test driver, the OpenNebula driver (removed in the meantime) and the
    vbox driver were already updating the domain ID correctly in
    domainCreate().
    
    Copy over the ID in qemuDomainCreateWithFlags() to fix this for the qemu
    driver, too.
    
    Fixes: de3aadaa ("drivers: add virDomainCreateWithFlags if virDomainCreate exists")
    Reported-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
    Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
    Tested-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>
    Reviewed-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>