ceph-pr-docs: add annotation to build result

ceph-pr-docs: add annotation to build result

* do not "set -e", so the script does not exit immediately. instead
  use a variable of "succeed" to store true if the document is built
  successfully, and false otherwise
* feed the output of the sphinx-build to github-check tool, so it
  is able to parse and call the GitHub Check API to update the
  Check web page on the PR if the test fails.

Signed-off-by: Kefu Chai <kchai@redhat.com>