increase hpo parallel training jobs to 2 (#146)

Issue #, if available:
see conversation on #144. Although I don't see any technical reason to have 2 training jobs in this test, I will disagree and commit to increasing the parallel job count for now so the jobs do not run serially

Testing:
PR build

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Author: surajkota

test/e2e/resources/xgboost_hpojob.yaml

@@ -11,7 +11,7 @@ spec:
       metricName: validation:error
     resourceLimits:
       maxNumberOfTrainingJobs: 2
-      maxParallelTrainingJobs: 1
+      maxParallelTrainingJobs: 2
     parameterRanges:
       integerParameterRanges:
       - name: num_round
@@ -65,4 +65,4 @@ spec:
     - key: environment
       value: testing
     - key: customer
-      value: test-user
+      value: test-user