[WIP] Remove absolute dependence of adal

[micw523]

Fixes kubernetes-client/python#668
Fixes kubernetes-client/python#645
Will need to be updated concurrently with a PR from the main repo.
Task list:
[x] Use try / except to handle adal import
[ ] modify setup file to add the adal option [main repo]
[ ] add adal option to the install section of documentation [main repo]
[ ] change the main test interface to install k8s with adal
[ ] add a test env and a minimal test that does not include adal

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[micw523]

/uncc mbohlool
/uncc yliaog
/hold
/joke

[k8s-ci-robot]

@micw523: Did you hear about the guy who invented Lifesavers? They say he made a mint.

In response to this:

/uncc mbohlool
/uncc yliaog
/hold
/joke

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[dims]

@micw523 @iamneha since this is a WIP and has a task list ...

• @micw523 can you please turn the task list into issues?
• Also let's close this and leave 108 as we need to pick one or the other :)

Sounds good?