nsxv3: stacking failed on compute node

On compute node, the stacking process failed with error. We don't need to check DHCP profile on a compute node.

2017-05-17 22:38:33.324 | ++/opt/stack/vmware-nsx/devstack/lib/vmware_nsx_v3:init_vmware_nsx_v3:217 die 217 'DHCP profile needs to be configured!'
2017-05-17 22:38:33.344 | ++functions-common:die:186 local exitcode=0
2017-05-17 22:38:33.366 | [Call Trace]
2017-05-17 22:38:33.366 | ./stack.sh:1210:run_phase
2017-05-17 22:38:33.366 | /home/nicira/devstack/functions-common:2001:run_plugins
2017-05-17 22:38:33.367 | /home/nicira/devstack/functions-common:1968:source
2017-05-17 22:38:33.367 | /opt/stack/vmware-nsx/devstack/plugin.sh:57:init_vmware_nsx_v3
2017-05-17 22:38:33.367 | /opt/stack/vmware-nsx/devstack/lib/vmware_nsx_v3:217:die
2017-05-17 22:38:33.374 | [ERROR] /opt/stack/vmware-nsx/devstack/lib/vmware_nsx_v3:217 DHCP profile needs to be configured!