[rotang] Enable updates to the rotation calendar if rotation is enabled.

Also changed here is to not add the shift name to Calendar events with only one shift

Bug: 845549
Change-Id: Ia87ee302deb8af2aa7441f56e5037097d61058c6
Reviewed-on: https://chromium-review.googlesource.com/c/1335367
Reviewed-by: Tiffany Zhang <zhangtiff@chromium.org>
Commit-Queue: Ola Karlsson <olakar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#19033}