Generated shell scripts for maven use a typical bash
if syntax which is not recognised by sh.
As a result the execution was failing on Gerrit CI.
(see [1])
Use bash as script interpreter to assure the correct
execution of the if statement.
[1]: https://goo.gl/3T5w5u
Change-Id: Id713a24d9cd6df145790769d014de6a66e64dace