tox: add mypy env and some minor improvments

- add mypy env
- pytest accepts a parameter
- `generate` builds the module in the output directory

.gitignore

@@ -0,0 +1 @@
+output/

tox.ini

@@ -8,7 +8,7 @@ install_command = pip install {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands =
-    pytest -vvv {posargs} {toxinidir}/vmware_rest_code_generator/
+    pytest -vvv {posargs:{toxinidir}/vmware_rest_code_generator/}
 
 [testenv:black]
 deps =
@@ -25,6 +25,12 @@ commands =
   black -v --check {toxinidir}/vmware_rest_code_generator
   flake8 {posargs} {toxinidir}/vmware_rest_code_generator
 
+[testenv:mypy]
+deps =
+  mypy
+commands =
+  mypy vmware_rest_code_generator/
+
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
 show-source = True
@@ -35,4 +41,4 @@ exclude = .git,.tox,tests/unit/compat/
 
 [testenv:generate]
 usedevelop = True
-commands = vmware_rest_code_generator_refresh_modules --target-dir {temp_dir}/modules
+commands = vmware_rest_code_generator_refresh_modules --target-dir {toxinidir}/output