qga/vss-win32: Add VSS provider unregistration retry

qga/vss-win32: Add VSS provider unregistration retry

This commit improves the QGA VSS provider installation flow by attempting to unregister the VSS provider if it's already
found during installation. This allows for a retry of installation even if a previous unregistration failed or was not performed.
This will prevent inconsistencies between QGA and QGA-VSS versions.
Before this commit, QGA can use QGA-VSS from the previous installation.

Signed-off-by: Elizabeth Ashurov <eashurov@redhat.com>
Reviewed-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>
Message-ID: <20250618091806.170110-1-eashurov@redhat.com>
Signed-off-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>