[target allocator] Fix flaky server test in targets handler

[matej-g]

Signed-off-by: Matej Gera matej.gera@coralogix.com

We were occasionally seeing a failure in TestServer_TargetsHandler/Multiple_entry_target_map_of_same_job_with_label_merge with the following output:

    server_test.go:177: 
        	Error Trace:	/home/runner/work/opentelemetry-operator/opentelemetry-operator/cmd/otel-allocator/server/server_test.go:177
        	Error:      	Not equal: 
        	            	expected: []*target.Item{(*target.Item)(0xc000717d40), (*target.Item)(0xc000717da0)}
        	            	actual  : []*target.Item{(*target.Item)(0xc00017a840), (*target.Item)(0xc00017a8a0)}
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1,2 +1,16 @@
        	            	 ([]*target.Item) (len=2) {
        	            	+ (*target.Item)({
        	            	+  JobName: (string) "",
        	            	+  Link: (target.LinkJSON) {
        	            	+   Link: (string) ""
        	            	+  },
        	            	+  TargetURL: ([]string) (len=1) {
        	            	+   (string) (len=9) "test-url2"
        	            	+  },
        	            	+  Labels: (model.LabelSet) (len=1) {
        	            	+   (model.LabelName) (len=10) "test_label": (model.LabelValue) (len=11) "test-value2"
        	            	+  },
        	            	+  CollectorName: (string) "",
        	            	+  hash: (string) ""
        	            	+ }),
        	            	  (*target.Item)({
        	            	@@ -14,16 +28,2 @@
        	            	   hash: (string) ""
        	            	- }),
        	            	- (*target.Item)({
        	            	-  JobName: (string) "",
        	            	-  Link: (target.LinkJSON) {
        	            	-   Link: (string) ""
        	            	-  },
        	            	-  TargetURL: ([]string) (len=1) {
        	            	-   (string) (len=9) "test-url2"
        	            	-  },
        	            	-  Labels: (model.LabelSet) (len=1) {
        	            	-   (model.LabelName) (len=10) "test_label": (model.LabelValue) (len=11) "test-value2"
        	            	-  },
        	            	-  CollectorName: (string) "",
        	            	-  hash: (string) ""
        	            	  })

This is presumable due to nondeterministic order of items, which on some test runs seem to change. Using ElementsMatch method instead of Equal will ensure the order of items is not decisive for passing the test.

Tested locally with -count=100 flag to catch the error and subsequently to test the fix.

cc @jaronoff97