cleanup: use same clang-tidy in all repositories (googleapis/google-cloud-cpp-common#206)

Use the clang-tidy distributed with Fedora (currently clang-tidy-9) in
this repository. I am planning to make similar changes in the other
repositories and bring all our `clang-tidy` builds to use the same
versions of `clang-format`, `clang-tidy`, `doxygen`, `buildifier`,
`shellcheck`, and `cmake_format`.

I also updated the clang-tidy configuration to match the newer repos
(`-pubsub` and `-spanner`), and cleaned up any errors found in the
files.

Finally, fixed a number of Doxygen comments that used `<U>` (for a
template parameter) which Doxygen thought was an unordered list or
something.

Author: coryan

release/release.sh

@@ -86,7 +86,7 @@ trap exit_handler EXIT
 # we make sure it's installed early on so we don't fail after completing part
 # of the release. We also use 'hub' to do the clone so that the user is asked
 # to authenticate at the beginning of the process rather than at the end.
-if ! which hub > /dev/null; then
+if command -v hub > /dev/null; then
   echo "Can't find 'hub' command"
   echo "Maybe run: sudo apt install hub"
   echo "Or build it from https://github.com/github/hub"