[Android Tests] Use EmbeddedTestServerTestRule for notification tests

- Rather than using an embedded test server directly within
NotificationTestRule, use an EmbeddedTestServerTestRule from those
tests that use this rule explicitly.

- This is a precursor to being able to use PermissionTestRule from
NotificationPlatformBridgeTest in order to re-enable the permission
tests (because PermissionTestRule uses an EmbeddedServerTestRule
internally too atm and they clash).

Bug: 865034
Change-Id: I2cc61938acf5cd449dc2a5fecdec69e0a1167c6d
Reviewed-on: https://chromium-review.googlesource.com/1142148
Reviewed-by: Helen Li <xunjieli@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Anita Woodruff <awdf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576818}
4 files changed