Refactor create_ and update_ methods for VIPs and health_monitors

Remove the following methods from json and xml network clients:
    -create_vip;
    -update_vip;
    -create_health_monitor;
    -update_halth_monitor;

Move the update_ methods to network/base and modify create_ methods.

Modify test_load_balancer accordingly.

Change-Id: I4eaad4270780b99181a357115d4061ae5ed6bc35
Merge "Refactor create_ and update_ methods for VIPs and health_monitors"