Adds condition to handle QoS extension in sriov_agent.ini template

When Neutron QoS is enabled, the QoS extension needs to be defined
in the sriov_agent.ini file.

Closes-Bug: #2041863
Change-Id: Id0de181df06a9e382a1483b32c12a8b5da1b71a9
Signed-off-by: German Espinoza <gespinoza@whitestack.com>

ansible/roles/neutron/templates/sriov_agent.ini.j2

+{% if enable_neutron_qos | bool %}
+[agent]
+extensions = qos
+{% endif %}
+
 [sriov_nic]
 # 'physical_device_mappings' is a comma separated list
 # Maps a physical network to network inferface used for SRIOV