Do not kill all on task delete by default

- Still KillAll if the task uses the hosts pid namespace
 - Test for both host pid namespace and normal cases

Co-authored-by: Oliver Stenbom <ostenbom@pivotal.io>
Co-authored-by: Georgi Sabev <georgethebeatle@gmail.com>
Signed-off-by: Oliver Stenbom <ostenbom@pivotal.io>

runtime/v1/linux/proc/init.go

@@ -249,7 +249,6 @@ func (p *Init) setExited(status int) {
 }
 
 func (p *Init) delete(context context.Context) error {
-	p.KillAll(context)
 	p.wg.Wait()
 	err := p.runtime.Delete(context, p.id, nil)
 	// ignore errors if a runtime has already deleted the process