Fix longevity test runs

Problem:
Running longevity test mistakenly runs all other NFRs
make start-longevity-test and make stop-longevity-test mistakenly
executes all NFRs. Only longevity test must run.

Solution:
Problem was introduced in 8671fb7
revert the affected change.

Testing:
- Ran make start-longevity-test and make stop-longevity-test successfully.

CLOSES - #2064

Author: pleshakov

tests/Makefile

@@ -100,12 +100,12 @@ nfr-test: ## Run the NFR tests on a GCP VM
 	NFR=true bash scripts/run-tests-gcp-vm.sh
 
 .PHONY: start-longevity-test
-start-longevity-test: START_LONGEVITY=true
-start-longevity-test: nfr-test ## Start the longevity test to run for 4 days in GKE
+start-longevity-test:  ## Start the longevity test to run for 4 days in GKE
+	START_LONGEVITY=true $(MAKE) nfr-test
 
 .PHONY: stop-longevity-test
-stop-longevity-test: STOP_LONGEVITY=true
-stop-longevity-test: nfr-test ## Stop the longevity test and collects results
+stop-longevity-test: ## Stop the longevity test and collects results
+	STOP_LONGEVITY=true $(MAKE) nfr-test
 
 .PHONY: .vm-nfr-test
 .vm-nfr-test: ## Runs the NFR tests on the GCP VM (called by `nfr-test`)