fix(tests): Make IE10/IE11 pass all the mocha tests.

* IE10 passes with no additional work.
* IE11 requires mouse interaction for the tests to complete correctly.

issue #1334
Only gather entropy from the server if the browser does not support crypto.getRandomValues.
Merge pull request #1355 from mozilla/issue-1334-ie-test-failures

fix(tests): Make IE10/IE11 pass all the mocha tests.