tests: don't immediately exit on error in wait_for_cilium_shutdown
tests: don't immediately exit on error in wait_for_cilium_shutdown

The error state is already handled there by timing out. Also bump the
timeout and use pgrep.

Related: #2239 (Build failure: 20-cidr-limit failed while waiting for Cilium to shut down)
Signed-off-by: Alexander Alemayhu <e46fc836cca3acec03944314d1457c2ae6c68ef3@alemayhu.com>

cilium/cilium,cilium-team/cilium,cilium/cilium,eloycoto/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,michi-covalent/cilium,scanf/cilium,eloycoto/cilium,michi-covalent/cilium,tgraf/cilium,scanf/cilium,scanf/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,eloycoto/cilium,tgraf/cilium,tklauser/cilium,scanf/cilium,scanf/cilium,eloycoto/cilium,cilium-team/cilium,cilium/cilium,eloycoto/cilium,eloycoto/cilium,tgraf/cilium,scanf/cilium,scanf/cilium,eloycoto/cilium