travis: Add python path for environments

When running in travis-ci, we want to pass environment configuration to
the tests. These reside in a path available through PYTHONPATH, so let's
define that one to point to the unit test repo.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Tom Rini <trini@konsulko.com>

.travis.yml

@@ -49,6 +49,7 @@ install:
 env:
   global:
     - PATH=/tmp/dtc:/tmp/uboot-test-hooks/bin:$PATH
+    - PYTHONPATH=/tmp/uboot-test-hooks/py/travis-ci
     - BUILD_DIR=build
     - HOSTCC="cc"
     - HOSTCXX="c++"