tests: make tests work on python3

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

tests/gpio_checks.py

@@ -22,6 +22,8 @@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
+from __future__ import print_function
+
 import mraa as m
 import unittest as u
 import os, re, sys