Update some DRMEngine tests to ES6
Update some DRMEngine tests to ES6

While working with DrmEngine I broke some tests. Why looking into what
part of the tests I broke I updated the tests to ES6.

Issue #1337
Change-Id: Ic865585c7ab0e8b858ef45fb02f1bcd0db6bcce2

shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player