Change the way we ignore coverage.

For the integration tests we are not interested in holding the 90%
coverage bar. Since we run them in isolation it doesn't report coverage
correctly and even setting a low threshold will fail the build. If we
set IGNORE_COVERAGE=-  then the exit code of coverage result will be
ignored.

Author: Ignacio Quintero

tox.ini

@@ -32,12 +32,11 @@ passenv =
     AWS_ACCESS_KEY_ID
     AWS_SECRET_ACCESS_KEY
     AWS_SESSION_TOKEN
-    COVERAGE_THRESHOLD
 # {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 py.test {posargs}
-    coverage report --fail-under={env:COVERAGE_THRESHOLD:90} --omit */tensorflow/tensorflow_serving/*
+    {env:IGNORE_COVERAGE:} coverage report --fail-under=90 --omit */tensorflow/tensorflow_serving/*
 deps =
     pytest
     pytest-cov