[sensors] Improve the generic sensors current layout tests.

Move all the tests that are going to be common in a single file.
Each of the sensor type will call a function to get the generic
tests to run. Specific sensor test can still be added in their
respective html files.

BUG=606766

Review-Url: https://codereview.chromium.org/2494773004
Cr-Commit-Position: refs/heads/master@{#431960}
2 files changed