[codespell] fix final typos and enable ci

This chnage adds the pre-commit config and
tox targets to run codespell both indepenetly
and via the pep8 target.

This change correct all the final typos in the
codebase as detected by codespell.

Change-Id: Ic4fb5b3a5559bc3c43aca0a39edc0885da58eaa2

tox.ini

@@ -107,15 +107,25 @@ extras =
 commands =
   bash tools/mypywrap.sh {posargs}
 
+[testenv:codespell]
+description =
+  Run codespell to check spelling.
+deps =
+  pre-commit
+commands =
+  pre-commit run codespell --all-files --show-diff-on-failure
+
 [testenv:pep8]
 description =
   Run style checks.
 deps =
   {[testenv]deps}
+  {[testenv:codespell]deps}
   autopep8
 extras =
 commands =
   {[testenv:mypy]commands}
+  {[testenv:codespell]commands}
   # check if autopep8 would alter the formatting but don't actually change it
   # so we can gate on this in the ci
   autopep8 --exit-code --max-line-length=79 --diff -r nova doc setup.py