Make shellcheck happy in DDoS releated scripts #283

Job	Run time
Setup variables	3s
Build controller image	2m 57s
Build node images (debian10)	1m 59s
Build node images (debian11)	2m 37s
Build node images (ubuntu16)	1m 45s
Build node images (ubuntu18)	2m 6s
Build node images (ubuntu20)	2m 29s
test_node_and_controller (debian10)	2m 45s
test_node_and_controller (debian11)	2m 50s
test_node_and_controller (ubuntu16)	3m 1s
test_node_and_controller (ubuntu18)	2m 44s
test_node_and_controller (ubuntu20)	2m 48s
statusCheck	1s
push_node	0s
push_controller	0s
	28m 5s

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