Re-enable disabled VR browser test

Re-enables WebVrBrowserTestOpenVrDisabled.TestWebVrNoDevicesWithoutOpenVr
and increases the timeout that was flakily being hit when many tests
were run in parallel.

Bug: 890380
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Iebb10f25848ac0ab3a2913fff4e35dad919fd4bc
Reviewed-on: https://chromium-review.googlesource.com/1252642
Reviewed-by: Bill Orr <billorr@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595266}