qemu: Move ParamsCheck closer to ParamsApply on Src side

qemu: Move ParamsCheck closer to ParamsApply on Src side

We reached the point when qemuMigrationParamsApply is the only API which
sends migration parameters and capabilities to QEMU. Thus all but the
TLS parameters can be set before we ask QEMU for the current values of
all parameters in qemuMigrationParamsCheck.

Supported migration capabilities are queried as soon as libvirt connects
to QEMU monitor so we can check them anytime.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>