add openstack CPI multi manual networks support for ubuntu 14.04 using g...

...o BOSH agent.

The changes are as follows:

In OpenStack CPI, network_configurator.rb is modified, where we changed the “network_type” validation logic, and parsed the configuration to obtain and record the multipl enetowkr ids (NICs) that are manually configured.

In Ruby Go_agent, Ubuntu_net_manager.go is modified, to check how many NICs are available based on information in  "/sys/class/net/xxx/devices", and change the configuration file under "/etc/network/interfaces " for the manually configured multiple networks to take effect.
make sure that err is not returned from SetupDhcp (also in tests below)