Increase timeout waiting for server for ros2 client in tests

[dhood]

4s is not always enough, e.g.:
http://ci.ros2.org/view/packaging/job/packaging_linux-aarch64/195/testReport/junit/(root)/test_dynamic_bridge__rmw_fastrtps_cpp_RelWithDebInfo/test_dynamic_bridge_srv_1to2/:

(test_dynamic_bridge_srv_1to2__dynamic_bridge) pid 43970: ['/opt/ros/kinetic/env.sh', '/home/rosbuild/ci_scripts/ws/build/ros1_bridge/dynamic_bridge'] (stderr > stdout, all > console)
(test_dynamic_bridge_srv_1to2__ros1server) pid 43973: ['/opt/ros/kinetic/env.sh', '/home/rosbuild/ci_scripts/ws/build/ros1_bridge/test_ros1_server'] (stderr > stdout, all > console)
(test_dynamic_bridge_srv_1to2__ros2client) pid 43981: ['/home/rosbuild/ci_scripts/ws/build/ros1_bridge/test_ros2_client_cpp'] (stderr > stdout, all > console)
[test_dynamic_bridge_srv_1to2__ros1server] ?[31m[ERROR] [1506936168.263634670]: [registerPublisher] Failed to contact master at [localhost:11311].  Retrying...?[0m
[test_dynamic_bridge_srv_1to2__dynamic_bridge] ?[31m[ERROR] [1506936168.361192670]: [registerPublisher] Failed to contact master at [localhost:11311].  Retrying...?[0m
[test_dynamic_bridge_srv_1to2__ros2client] terminate called after throwing an instance of 'std::runtime_error'
[test_dynamic_bridge_srv_1to2__ros2client]   what():  Service is not available
(test_dynamic_bridge_srv_1to2__ros2client) rc -6

ci_packaging_linux:
ci_packaging_linux-aarch64:

[mikaelarguedas]

lgtm