qemu: Adds support for devices with dynamic params to qdevices.

This patch make qdevice more verbose during qcontainer comparison.
Also this patch add support for dynamic params in general devices
like QStringDevice and QCustomDevice and for devices classed inherited from them.

It sets cmdline with and without dynamic params for QStringDevice.
dev = QStringDevice(dev_type="xxx", cmdline="xxx:dynamicparam",
                                    cmdline_nd="xxx:DYN")

It allows specification which param is dynamic for QCustomDevice
dev = QCustomDevice(dev_type="xxx")
dev.set_param(name, value, something, dynamic True/False) default is true.

Comparison of qcontainer using == works as usual it compare all params
without dynamic params.

Some of qemu devices needs some kind of preparation before
start of qemu vm. Unfortunately there preparatory work are
done during creation of devices. For example network tap devices,
port redir, etc.
  It should be divided in some later patch.

Signed-off-by: Jiří Župka <jzupka@redhat.com>