This patch removes duplicate internal copies of constants in the structs
package which are also defined in the api package. The api.KVOp type
with all its values for the TXN endpoint and the api.HealthXXX constants
are now used throughout the codebase.
This resulted in some circular dependencies in the testutil package
which have been resolved by copying code and constants and moving the
WaitForLeader function into a separate testrpc package.
Assuming the following output from a consul agent:
```
==> Consul agent running!
Version: 'v0.7.3-43-gc5e140c-dev (c5e140c+CHANGES)'
Node ID: '40e4a748-2192-161a-0510-9bf59fe950b5'
Node name: 'myhost'
```
it is now possible to lookup nodes by their Node Name or Node ID, or a
prefix match of the Node ID, with the following caveats re: the prefix
match:
1) first eight digits of the Node ID are a required minimum (eight was
chosen as an arbitrary number)
2) the length of the Node ID must be an even number or no result will be
returned.
```
% dig @127.0.0.1 -p 8600 myhost.node.dc1.consul.
myhost.node.dc1.consul. 0 IN A 127.0.0.1
% dig @127.0.0.1 -p 8600 40e4a748-2192-161a-0510-9bf59fe950b5.node.dc1.consul.
40e4a748-2192-161a-0510-9bf59fe950b5.node.dc1.consul. 0 IN A 127.0.0.1
% dig @127.0.0.1 -p 8600 40e4a748.node.dc1.consul.
40e4a748.node.dc1.consul. 0 IN A 127.0.0.1
% dig @127.0.0.1 -p 8600 40e4a74821.node.dc1.consul.
40e4a74821.node.dc1.consul. 0 IN A 127.0.0.1
% dig @127.0.0.1 -p 8600 40e4a748-21.node.dc1.consul.
40e4a748-21.node.dc1.consul. 0 IN A 127.0.0.1
```
We always did an update before which caused excessive watch churn, even
with our new fine-grained queries. This does a diff any only updates the
node and service records if something actually changed.
Frank Schroeder