Fix bug in --install-addons flag

[priyawadhwa]

Respect --install-addons flag, don't install anything if it is false

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: priyawadhwa

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[priyawadhwa]

/ok-to-test

[minikube-pr-bot]

All Times minikube: [ 94.713464 93.878937 93.804372]
All Times Minikube (PR 6696): [ 93.395557 91.442822 92.642918]

Average minikube: 94.132257
Average Minikube (PR 6696): 92.493766

Averages Time Per Log

+----------------------+-----------+--------------------+
|         LOG          | MINIKUBE  | MINIKUBE (PR 6696) |
+----------------------+-----------+--------------------+
| minikube v           |  0.202234 |           0.203729 |
| Creating kvm2        | 19.875490 |          19.984877 |
| Preparing Kubernetes | 50.586381 |          49.557570 |
| Pulling images       |           |                    |
| Launching Kubernetes | 21.096823 |          20.947517 |
| Waiting for cluster  |  0.391112 |           0.239539 |
+----------------------+-----------+--------------------+

[medyagh]

unit test failure is not related to your PR, travis is crazy today