utils_spice: Adding new functions with support for Windows

We want to add support for running spice tests on
Windows client by being able to install usbclerk
and also kill remote-viewer window if it's open.
Also, adding kill_app function to kill an
application on a VM.

Reviewed by: Swapna Krishnan <skrishna@redhat.com>
Merge pull request #1876 from swapnakrishnan2k/add_new_func_utils_spice

Adding new functions with support for Windows