VIP creation fails if ip address is not specified.

Neutron Client allows creation of VIP by specifying only
a subnet. In that case a free ip from that subnet will be
asigned.
When creating the VIP from Horizon, if the ip address is not
set on them form, the request for VIP creation will include
an empty address and fail.
If the address is not set or empty, don't send that key
since it's not mandatory.

Change-Id: Id9b8f4aa187eae65f5b87c742309e0e39c804208
Closes-Bug: #1252811
Merge "VIP creation fails if ip address is not specified."