Add multi-target support to win_pkg.py install function

This commit adds the "pkgs" argument to the install() function, and also
fixes a traceback in the remove() function when a package which does not
exist is used.

Note that this still does not resolve the issue with pkg states, because
the package names discovered in list_pkgs are still the full name of the
package and not the name as defined in the winrepo.
Merge pull request #5642 from terminalmage/issue5422

Add multi-target support to win_pkg.py install function