Move zuul-legacy-jobs.yaml jobs to Bionic

As part of migration all legacy base jobs to bionic
- https://review.openstack.org/#/c/639096/
- https://etherpad.openstack.org/p/legacy-job-bionic

This commit moves the legacy jobs defined in zuul-legacy-jobs.yaml
to Bionic by removing the overridden nodeset. From now onwards
these jobs will use nodeset defined in their parents job which is
Bionic from stein onwards and xenial for rest all stable branches.

Change-Id: Ic29c878d38886e9a8d5b4266cd9a9a25dc0030b5

zuul.d/zuul-legacy-jobs.yaml

@@ -132,7 +132,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/cinder
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-grenade-dsvm-cinder-mn-sub-volbak
@@ -145,7 +144,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/cinder
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-grenade-dsvm-cinder-mn-sub-volschbak
@@ -157,7 +155,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/cinder
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-grenade-dsvm-neutron-forward
@@ -181,7 +178,6 @@
       - openstack-infra/devstack-gate
       - openstack/neutron
       - openstack/neutron-fwaas
-    nodeset: legacy-ubuntu-xenial-2-node
     branches: ^(?!stable/(newton|ocata)).*$
 
 - job:
@@ -215,7 +211,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/neutron
-    nodeset: legacy-ubuntu-xenial-2-node
     branches: ^(?!stable/(newton|ocata)).*$
 
 - job:
@@ -228,7 +223,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/neutron
-    nodeset: legacy-ubuntu-xenial-2-node
     branches: ^(?!(driverfixes|stable/(newton|ocata))).*$
 
 - job:
@@ -241,7 +235,6 @@
       - openstack-dev/grenade
       - openstack-infra/devstack-gate
       - openstack/neutron
-    nodeset: legacy-ubuntu-xenial-2-node
     branches: ^(?!stable/(newton|ocata)).*$
 
 - job:
@@ -414,7 +407,6 @@
     run: playbooks/legacy/laravel-openstackid-release-branch/run.yaml
     post-run: playbooks/legacy/laravel-openstackid-release-branch/post.yaml
     timeout: 1800
-    nodeset: legacy-ubuntu-xenial
 
 - job:
     name: legacy-laravel-openstackid-release-master
@@ -422,7 +414,6 @@
     run: playbooks/legacy/laravel-openstackid-release-master/run.yaml
     post-run: playbooks/legacy/laravel-openstackid-release-master/post.yaml
     timeout: 1800
-    nodeset: legacy-ubuntu-xenial
 
 - job:
     name: legacy-laravel-openstackid-unittests
@@ -430,7 +421,6 @@
     run: playbooks/legacy/laravel-openstackid-unittests/run.yaml
     post-run: playbooks/legacy/laravel-openstackid-unittests/post.yaml
     timeout: 1800
-    nodeset: legacy-ubuntu-xenial
 
 - job:
     name: legacy-logstash-filters
@@ -793,7 +783,6 @@
       - openstack/neutron
       - openstack/neutron-fwaas
       - openstack/tempest
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-neutron-fwaas-v2-dsvm-tempest
@@ -818,7 +807,6 @@
       - openstack/neutron
       - openstack/neutron-fwaas
       - openstack/tempest
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-neutronclient-test-dsvm-functional
@@ -1619,7 +1607,6 @@
       - openstack-infra/devstack-gate
       - openstack/neutron
       - openstack/tempest
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-tempest-dsvm-neutron-dvr-multinode-scenario
@@ -1631,7 +1618,6 @@
       - openstack-infra/devstack-gate
       - openstack/neutron
       - openstack/tempest
-    nodeset: legacy-ubuntu-xenial-2-node
 
 - job:
     name: legacy-tempest-dsvm-neutron-full
@@ -1666,6 +1652,7 @@
       - openstack-infra/devstack-gate
       - openstack/neutron
       - openstack/tempest
+    nodeset: legacy-ubuntu-xenial
 
 - job:
     name: legacy-tempest-dsvm-neutron-full-opensuse-423