KVM: selftests: Rename vm_handle_exception

Rename the vm_handle_exception function to a name that indicates more
clearly that it installs something: vm_install_exception_handler.

Reported-by: kernel test robot <oliver.sang@intel.com>
Suggested-by: Marc Zyngier <maz@kernel.org>
Suggested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210611011020.3420067-2-ricarkol@google.com