CLSTACK-784 - Deassociate IP address if enabling static nat fails

Steps to reproduce the issue

(1) create a vpc (vpc-001) and a vpc tier (vpc-001-001)

(2) create a vm (vm-001-001) in vpc-001-001

(3) acquire a public ip (ip-1) and enable static nat to vm-001-001,
operation succeeds.

(4) acquire a public ip (ip-2) and enable static nat to vm-001-001,
operation fails but the ip is still assigned to vpc tier vpc-001-001.
Note down the ip address and the id of it.

(5) create another vpc tier vpc-001-002, and vm (vm-001-002) in the tier

(6) enabled ip-2 static nat to vm-001-002, operation should succeed

Author: ravening

server/src/main/java/com/cloud/network/rules/RulesManagerImpl.java

@@ -500,6 +500,7 @@ private boolean enableStaticNat(long ipId, long vmId, long networkId, boolean is
                         s_logger.debug("The ip is not associated with the VPC network id=" + networkId + ", so assigning");
                         try {
                             ipAddress = _ipAddrMgr.associateIPToGuestNetwork(ipId, networkId, false);
+                            performedIpAssoc = true;
                         } catch (Exception ex) {
                             s_logger.warn("Failed to associate ip id=" + ipId + " to VPC network id=" + networkId + " as " + "a part of enable static nat");
                             return false;