Add installation of mypy stubs packages

The cinder-mypy job is failing because library stubs aren't installed
for requests [0].  Modify the mypywrap.sh to accept options specified
in an environment variable named OS_MYPY_OPTS to the mypy invocation,
and set this var in tox.ini.

The value is "--install-types --non-interactive" which is suitable for
CI purposes, and seems to make sense for local tox use as well [1].
The downside is it basically runs mypy twice, once to determine
whether there are any library stubs missing and then install them, and
againto do the actual check.  If we don't want this setting in
tox.ini, we can move it to .zuul.yaml for the cinder-mypy job run.

Also, update the version of mypy in test-requirements to a version
that supports the above options.

And, run mypy in its own env (instead of reusing pep8) so that the
tox logs are preserved during CI runs.

[0] https://zuul.opendev.org/t/openstack/build/b66ee6c21e594940941585b0e9e5082a
[1] https://mypy.readthedocs.io/en/stable/running_mypy.html#library-stubs-not-installed

Change-Id: Id69cb519ee7300b33ff087de4e7d46cdad67d162

test-requirements.txt

@@ -21,5 +21,5 @@ testtools>=2.4.0 # MIT
 # so we need to pin it here to a known working version
 bandit==1.6.0 # Apache-2.0
 doc8>=0.8.1 # Apache-2.0
-mypy>=0.782 # MIT
+mypy>=0.910 # MIT
 moto>=1.3.15 # Apache-2.0

tools/mypywrap.sh

@@ -17,8 +17,8 @@ export MYPYPATH=$ROOT_DIR/../cinder/tests/stubs/
 if [ $# -eq 0 ]; then
     # if no arguments provided, use the standard converted lists
     lines=$(grep -v '#' $ROOT_DIR/../mypy-files.txt)
-    python -m mypy ${lines[@]}
+    python -m mypy $OS_MYPY_OPTS ${lines[@]}
 else
     # else test what the user asked us to
-    python -m mypy $@
+    python -m mypy $OS_MYPY_OPTS $@
 fi

tox.ini

@@ -169,7 +169,8 @@ usedevelop = False
 [testenv:mypy]
 description =
   Run type checks.
-envdir = {toxworkdir}/pep8
+setenv =
+  OS_MYPY_OPTS=--install-types --non-interactive
 commands =
   {toxinidir}/tools/mypywrap.sh {posargs}