[API] Support per-tenant max loadbalancers

Note: Schema altering change

Adds a new table that allows maximum number of load balancers to
be set per tenant ID. If a value is not set, the global value is
used. The per-tenant value always overrides the global value.

Change-Id: Ib7911742510756e34a4ef0ecf9380abb2a759e8e
[API] Support for LB timeout options

NOTE: Database schema altering change.

Companion commit for commit 0eb56f. Timeout values (for client,
server, connect) and connect retry values can now be specified
in the UPDATE request. E.g.:

    {
      "hpcs_action": "UPDATE",
      "loadBalancers": [
         "protocol": "http",
         "options": {
             "client_timeout": "30000",
             "server_timeout": "30000",
             "connect_timeout": "30000",
             "connect_retries": "3"
         },
         ...
      ]
    }

Default values are saved to the LOADBALANCERS table in the database
if no values are given in the JSON message. The current defaults
match the defaults in the HAProxy worker driver so pre-existing LBs
will match new LBs.

Change-Id: I2edb67e462f314837fc89ac82eaf1140291a939e