infra: fix tox test dependencies and bump coverage threshold to 86%

Author: laurenyu

tox.ini

@@ -58,13 +58,12 @@ passenv =
     AWS_SESSION_TOKEN
     AWS_CONTAINER_CREDENTIALS_RELATIVE_URI
     AWS_DEFAULT_REGION
-
 # {posargs} can be passed in by additional arguments specified when invoking tox.
 # Can be used to specify which tests to run, e.g.: tox -- -s
 commands =
     coverage run --source sagemaker -m pytest {posargs}
-    {env:IGNORE_COVERAGE:} coverage report --fail-under=85 --omit */tensorflow/tensorflow_serving/*
-extras = test
+    {env:IGNORE_COVERAGE:} coverage report --fail-under=86 --omit */tensorflow/tensorflow_serving/*
+deps = .[test]
 
 [testenv:flake8]
 basepython = python3