Add unit tests

[CecileRobertMichon]

Currently coverage is 38%. We should add unit tests as much as possible and get closer to 100%. Good places to start:

• https://github.com/Azure/acs-engine/tree/master/pkg/acsengine, for example https://github.com/Azure/acs-engine/blob/master/pkg/acsengine/engine_test.go
• https://github.com/Azure/acs-engine/tree/master/pkg/operations/
• https://github.com/Azure/acs-engine/tree/master/cmd

[CecileRobertMichon]

Update: coverage is now 47% (https://codecov.io/gh/Azure/acs-engine). Codecov integration was added in #2719 to help us track coverage in PRs.

[CecileRobertMichon]

Coverage is now 53%

[mboersma]

Coverage is now 68%.

[tariq1890]

There is no such thing as "too many unit tests".

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.