Add tox target and configuration for codespell

Adds a tox target for codespell, `tox -e codespell`. Can optionally
be run as `tox -e codespell -- -w` to get automatic spelling fixes
applied where appropriate. Adds small amounts of configuration to
setup.cfg, including an ignore list of words.

Related-bug: #2047654
Change-Id: I98203b02a9c6b6fc36edd6b4bbcc7c92a634da8b

setup.cfg

@@ -71,3 +71,9 @@ tag_svn_revision = 0
 [extras]
 burnin-network-kazoo =
     kazoo>=2.8.0 # Apache-2.0
+
+[codespell]
+quiet-level = 4
+# Words to ignore:
+# cna: Intel CNA card
+ignore-words-list = cna

tox.ini

@@ -24,6 +24,15 @@ passenv =
     no_proxy
     NO_PROXY
 
+[testenv:codespell]
+description =
+  Run codespell to check spelling
+deps = codespell
+# note(JayF): {posargs} lets us run `tox -ecodespell -- -w` to get codespell
+#             to correct spelling issues in our code it's aware of.
+commands =
+  codespell {posargs}
+
 [testenv:functional]
 # Define virtualenv directory, port to use for functional testing, and number
 # of seconds to wait for the agent to come alive during functional testing.