add requirements.txt support to python unit test

Change-Id: Id54a1b7429795dffd482b962b4c7858445239609
diff --git a/jjb/python-unit.yaml b/jjb/python-unit.yaml
index f64801f..4cdad78 100644
--- a/jjb/python-unit.yaml
+++ b/jjb/python-unit.yaml
@@ -43,6 +43,12 @@
       - shell: |
           #!/usr/bin/env bash
           set -eux -o pipefail
+
+          if [ -f requirements.txt ]; then
+            echo "requirements.txt found, installing locally with pip"
+            pip install -r requirements.txt
+          fi
+
           echo "Performing nose2 tests"
           nose2 --verbose --coverage-report xml --coverage-report term --junit-xml