utest: add loxigen directory to front of sys.path

Python prepepnds apt-get installed packages even before PYTHONPATH. This caused
the parser unit tests to fail on machines with an older version of pyparsing
installed even though it's included in the repo.
diff --git a/Makefile b/Makefile
index 591aa79..133b6fb 100644
--- a/Makefile
+++ b/Makefile
@@ -87,9 +87,9 @@
 	@echo "INPUT_FILES=\"${INPUT_FILES}\""
 
 check:
-	PYTHONPATH=. ./utest/test_parser.py
-	PYTHONPATH=. ./utest/test_frontend.py
-	PYTHONPATH=. ./utest/test_test_data.py
+	./utest/test_parser.py
+	./utest/test_frontend.py
+	./utest/test_test_data.py
 
 check-py: python
 	PYTHONPATH=${LOXI_OUTPUT_DIR}/pyloxi:. python py_gen/tests/generic_util.py
diff --git a/utest/test_frontend.py b/utest/test_frontend.py
index 1f284b0..01b8270 100755
--- a/utest/test_frontend.py
+++ b/utest/test_frontend.py
@@ -26,7 +26,13 @@
 # EPL for the specific language governing permissions and limitations
 # under the EPL.
 
+import sys
+import os
 import unittest
+
+root_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)), '..')
+sys.path.insert(0, root_dir)
+
 import loxi_front_end.parser as parser
 import loxi_front_end.frontend as frontend
 from loxi_ir import *
diff --git a/utest/test_parser.py b/utest/test_parser.py
index cb22a9c..40d2913 100755
--- a/utest/test_parser.py
+++ b/utest/test_parser.py
@@ -26,7 +26,13 @@
 # EPL for the specific language governing permissions and limitations
 # under the EPL.
 
+import sys
+import os
 import unittest
+
+root_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)), '..')
+sys.path.insert(0, root_dir)
+
 import pyparsing
 import loxi_front_end.parser as parser
 
diff --git a/utest/test_test_data.py b/utest/test_test_data.py
index 16cf440..d0ed683 100755
--- a/utest/test_test_data.py
+++ b/utest/test_test_data.py
@@ -26,7 +26,13 @@
 # EPL for the specific language governing permissions and limitations
 # under the EPL.
 
+import sys
+import os
 import unittest
+
+root_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)), '..')
+sys.path.insert(0, root_dir)
+
 import test_data
 
 class DataFileTests(unittest.TestCase):