change: improve tox install times by not installing all deps when not needed

Moved to using deps to override the test extra being installed in
skip_install tox stages. Now only the needed deps are installed.

Improves install time by around 7x.

Closes aws#4591

Author: jmahlik

tox.ini

@@ -100,28 +100,33 @@ commands =
 [testenv:flake8]
 skipdist = true
 skip_install = true
+deps =
+    -r requirements/tox/flake8_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/flake8_requirements.txt
     flake8
 
 [testenv:pylint]
 skipdist = true
 skip_install = true
+deps =
+    -r requirements/tox/pylint_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/pylint_requirements.txt
     python -m pylint --rcfile=.pylintrc -j 0 src/sagemaker
 
 [testenv:spelling]
 skipdist = true
 skip_install = true
+deps =
+    -r requirements/tox/spelling_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/spelling_requirements.txt
     python -m pylint --rcfile=.pylintrc --disable all --enable spelling --spelling-dict en_US src/sagemaker/{posargs}
 
 [testenv:twine]
 # https://packaging.python.org/guides/making-a-pypi-friendly-readme/#validating-restructuredtext-markup
+skip_install = true
+deps =
+    -r requirements/tox/twine_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/twine_requirements.txt
     python setup.py sdist
     twine check dist/*.tar.gz
 
@@ -136,8 +141,9 @@ commands =
     sphinx-build -T -W -b html -d _build/doctrees-readthedocs -D language=en . _build/html
 
 [testenv:doc8]
+deps =
+    -r requirements/tox/doc8_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/doc8_requirements.txt
     doc8 --ignore-path tests/data/serve_resources/mlflow/pytorch/data/pickle_module_info.txt
 
 [testenv:black-format]
@@ -146,8 +152,9 @@ skip_install = true
 setenv =
     LC_ALL=C.UTF-8
     LANG=C.UTF-8
+deps =
+    -r requirements/tox/black_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/black_requirements.txt
     black ./
 
 [testenv:black-check]
@@ -156,8 +163,9 @@ skip_install = true
 setenv =
     LC_ALL=C.UTF-8
     LANG=C.UTF-8
+deps =
+    -r requirements/tox/black_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/black_requirements.txt
     black --diff --color --check ./
 
 [testenv:clean]
@@ -166,13 +174,20 @@ commands =
     coverage erase
 
 [testenv:typing]
+# Do not skip installation here, the extras are needed for mypy to get type info
+skip_install = false
+extras =
+    all
+deps =
+    -r requirements/tox/mypy_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/mypy_requirements.txt
     mypy src/sagemaker
 
 [testenv:docstyle]
+skip_install = true
+deps =
+    -r requirements/tox/pydocstyle_requirements.txt
 commands =
-    pip install --exists-action=w -r requirements/tox/pydocstyle_requirements.txt
     pydocstyle src/sagemaker
 
 [testenv:collect-tests]