Fix to work with API v2.

(1) Change URLs to use v2 instead of v1.

(2) Change get reply-object selector from value to node/value.

(3) Change set reply-object selector from index to node/modifiedIndex.

(4) Change etcd_set to use PUT instead of POST.

Also added MY_YAJL_GET_STRING to make gcc shut up about null arguments.

Signed-off-by: Jeff Darcy <jdarcy@redhat.com>