Execute test_initialize_network... with concurrency 1

Closes-Bug: #2113861
Change-Id: I635480cb087a75c8a4f2dbb30960b8aff8cf8b14
(cherry picked from commit 94f6d69)

Author: ralonsoh

tox.ini

@@ -85,7 +85,7 @@ description =
     Run functional gate tests that require sudo privileges.
 setenv = {[testenv:dsvm-functional]setenv}
 deps = {[testenv:dsvm-functional]deps}
-test_regex = .*MySQL\.|.*test_get_all_devices|.*TestMetadataAgent\.|.*BaseOVSTestCase\.|.*test_periodic_sync_routers_task|.*TestOvnNbSync.*|.*TestMaintenance|.*TestLogMaintenance|.*TestNBDbMonitor.*|.*test_ovn_client.*
+test_regex = .*MySQL\.|.*test_get_all_devices|.*TestMetadataAgent\.|.*BaseOVSTestCase\.|.*test_periodic_sync_routers_task|.*TestOvnNbSync.*|.*TestMaintenance|.*TestLogMaintenance|.*TestNBDbMonitor.*|.*test_ovn_client.*|.*test_initialize_network_segment_range_support_parallel_execution.*
 commands =
   bash {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
   stestr run --slowest --exclude-regex ({[testenv:dsvm-functional-gate]test_regex}|neutron.tests.functional.agent.l3.*) {posargs}