Lock aws-encryption-sdk and dynamodb-encryption-sdk downstream test dependencies (#4441)

* lock aws-encryption-sdk and dynamodb-encryption-sdk downstream tests to frozen dependencies

* explicitly identify test directory in dynanmodb-encryption-sdk downstream tests

* install the frozen dependencies after installing the package to force dependencies to the frozen set
diff --git a/.travis/downstream.d/aws-encryption-sdk.sh b/.travis/downstream.d/aws-encryption-sdk.sh
index 7363a83..044f70d 100755
--- a/.travis/downstream.d/aws-encryption-sdk.sh
+++ b/.travis/downstream.d/aws-encryption-sdk.sh
@@ -4,8 +4,8 @@
     install)
         git clone --depth=1 https://github.com/awslabs/aws-encryption-sdk-python
         cd aws-encryption-sdk-python
-        pip install -r test/requirements.txt
         pip install -e .
+        pip install -r test/upstream-requirements-py27.txt
         ;;
     run)
         cd aws-encryption-sdk-python
diff --git a/.travis/downstream.d/dynamodb-encryption-sdk.sh b/.travis/downstream.d/dynamodb-encryption-sdk.sh
index 891c616..196cd5b 100755
--- a/.travis/downstream.d/dynamodb-encryption-sdk.sh
+++ b/.travis/downstream.d/dynamodb-encryption-sdk.sh
@@ -4,12 +4,12 @@
     install)
         git clone --depth=1 https://github.com/awslabs/aws-dynamodb-encryption-python
         cd aws-dynamodb-encryption-python
-        pip install -r test/requirements.txt
         pip install -e .
+        pip install -r test/upstream-requirements-py27.txt
         ;;
     run)
         cd aws-dynamodb-encryption-python
-        pytest -m "local and not slow and not veryslow and not nope"
+        pytest test/ -m "local and not slow and not veryslow and not nope"
         ;;
     *)
         exit 1