Change expectation package log level to debug

[Jeffwan]

Resolve #89

Info level is kind of noisy and debug level is much better

Before

INFO[0011] need to create new service: worker-1          job=default.xgboost-dist-iris-test-train replica-type=worker uid=467fb419-962b-11ea-b670-026fb543c17c
INFO[0011] Setting expectations &expectation.ControlleeExpectations{add:1, del:0, key:"default/xgboost-dist-iris-test-train/worker/services", timestamp:time.Time{wall:0xbfa78c778e0631d8, ext:11414609468, loc:(*time.Location)(0x313bcc0)}}
INFO[0011] Update on create function xgboostjob-operator create object xgboost-dist-iris-test-train-worker-1
INFO[0011] Lowered expectations &expectation.ControlleeExpectations{add:-2, del:0, key:"default/xgboost-dist-iris-test-train/worker/pods", timestamp:time.Time{wall:0xbfa78c778a2968f0, ext:11349809202, loc:(*time.Location)(0x313bcc0)}}
INFO[0011] Controller xgboost-dist-iris-test-train created service xgboost-dist-iris-test-train-worker-1

After

INFO[0011] need to create new service: worker-1          job=default.xgboost-dist-iris-test-train replica-type=worker uid=467fb419-962b-11ea-b670-026fb543c17c
INFO[0011] Update on create function xgboostjob-operator create object xgboost-dist-iris-test-train-worker-1
INFO[0011] Controller xgboost-dist-iris-test-train created service xgboost-dist-iris-test-train-worker-1

[kubeflow-bot]

This change is 

[merlintang]

/lgtm

[Jeffwan]

Thanks for helping review.

/approve

[k8s-ci-robot]

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