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