virsh: Fix update dargs before call reference_function in VirshClosure

Update dargs with dict_like_instance but not overwrite values in
dargs, then call the reference_function use dargs.

Signed-off-by: Wayne Sun <gsun@redhat.com>
virsh: Add virsh itself group commands

Add functions for command 'cd', 'pwd', 'echo', 'exit' and 'quit'.

Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #1379 from waynesun09/virsh_itself

[PR updated] virsh: Add virsh itself group commands and fix dargs update problem in VirshClosure
Introduce virttest.tests

There are some high profile tests that are both used by
tests in different test providers, and comprise critical
virt-test functionality.

So, introduce a virttest.tests namespace, and put
unattended_install in it. Other tests will follow this
trend.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>