Bug 1770281: Fixing behat to accept confirm click of delete button

Added 'I click on "button" delete button' step so that the delete
buttons with 'confirm' popup get accepted

Change-Id: I0ec7d268cd275efb1398b58c26d87f3e8ffdc092
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
(cherry picked from commit cfed69ea)