Updates to Makefile

Change-Id: I30cf9808fe3389094bf581fa6159f9933e693a76
diff --git a/voltha/adapters/adtran_olt/Makefile b/voltha/adapters/adtran_olt/Makefile
index efa5fc7..7e88ba3 100644
--- a/voltha/adapters/adtran_olt/Makefile
+++ b/voltha/adapters/adtran_olt/Makefile
@@ -6,8 +6,8 @@
 VENVDIR=$(WORKING_DIR)venv
 TESTDIR=$(WORKING_DIR)test
 
-ADD_TO_PYTHONPATH := export PYTHONPATH=$(VOLTHA_DIR)/protos/third_party;
-IN_VENV=. '$(VENVDIR)/bin/activate'; $(ADD_TO_PYTHONPATH)
+ADD_TO_PYTHONPATH := export PYTHONPATH=$(PYTHONPATH):$(VOLTHA_DIR)protos/third_party;
+IN_VENV=. '$(VENVDIR)/bin/activate';
 
 PROFILING=--profile-svg
 DOT := $(shell command -v dot 2> /dev/null)
@@ -16,7 +16,7 @@
 PROFILING=
 endif
 
-RUN_PYTEST=$(IN_VENV) python -m pytest -vvlx $(PROFILING) --cov=$(WORKING_DIR) --cov-report term-missing --cov-report html
+RUN_PYTEST=$(IN_VENV) $(ADD_TO_PYTHONPATH) python -m pytest -vvlx $(PROFILING) --cov=$(WORKING_DIR) --cov-report term-missing --cov-report html
 
 $(VENVDIR):
 	@virtualenv -p python2 $(VENVDIR)