[ISTANBUL] Use integration istanbul branches for istanbul xtesting dockers

[ISTANBUL] Use integration istanbul branches for istanbul xtesting dockers

xtesting dockers have been released for istanbul (1.9.0)
but istanbul dockers are still rebuilt daily in jenkins.
I forgot to specify the branch of testsuite and integration
as a consequence daily istanbul xtesting dockers are using the master
branch. It explains why some istanbul tests look like master.
Some changes (DCAE refactoring) requires the istanbul version.
This patch just set properly the istanbul branch when building the dockers

Issue-ID: INT-2044

Signed-off-by: morganrol <morgan.richomme@orange.com>
Change-Id: I7a96cb8ed79fc0358bfd9f82fc186fd1dd98a9c4