Fix missing dict key from ec2 response.

[UtahDave]

Fixes #15900

ping @techhat

[UtahDave]

@rallytime Do we need some tests for this?

[rallytime]

Sure. I applied the Needs Testcase label so it doesn't get lost in the shuffle. :)

[ghost]

Test Failed.

If the failures are unrelated to your code, don't stress, a core developer will know these apart.
In the future, if possible, please branch off a passing commit to avoid false positives.
Refer to this link for build results: http://jenkins.saltstack.com/job/salt-pr-build/8121/

[techhat]

I'm seeing the same thing, and this looks to fix it. Thanks @UtahDave!

[techhat]

@UtahDave, this seems to have causes a regression; sometimes that key exists, and sometimes it does not. Will update when I have more info.

A fix for #15931 will also have to be posted when I have this worked out.