virt: qcontainer adds possibility to find device by params.

Allows to search specific device in qemu container by filter for
params. Created due to searching in the QStringDevices.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
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>
Merge pull request #1470 from autotest/gh-1348

Gh 1348