Use -y with 'pip uninstall'

'pip uninstall' will hang running stack.sh if it has to
prompt the user for input, use -y.

Change-Id: Ic94639e444b87fd3538463d5a51c01a0208a2ab2
Closes-bug: #1691172
diff --git a/inc/python b/inc/python
index a004217..4c443d6 100644
--- a/inc/python
+++ b/inc/python
@@ -362,7 +362,7 @@
         local sudo_pip="sudo -H"
     fi
     # don't error if we can't uninstall, it might not be there
-    $sudo_pip $cmd_pip uninstall $name || /bin/true
+    $sudo_pip $cmd_pip uninstall -y $name || /bin/true
 }
 
 # get version of a package from global requirements file