Disable failing tests
Generate expected HTML elements in unit tests

The statusbar logic expects the provided element to define a
`getContext` method, so a `canvas` element is the appropriate choice.
Comment out more failing tests
Fix issue with canvas usage

In order to avoid DOM exceptions, icons should not be draw to a canvas
until their image has completed loading.
Extend dialer Utils mock for unit tests
Disable failing tests
Initialize new stub for every dialer ussd test

Tests modify the state of the global `navigator.mozL10n` object, so this
object should be re-initialized before each test.