CA config and Client config: update format and semantics of probe

Refs: https://github.com/named-data/ndncert/wiki/NDNCERT-CA-Configuration

Change-Id: Ia0a8def6aea8565533a0f5364c44768d3849f18f
diff --git a/client.conf.sample b/client.conf.sample
index a0de72a..7e7d316 100644
--- a/client.conf.sample
+++ b/client.conf.sample
@@ -2,10 +2,9 @@
   "ca-list":
   [
     {
-        "ca-prefix": "/ndn/CA",
-        "ca-info": "NDN Testbed CA",
+        "ca-prefix": "/example",
+        "ca-info": "An example NDNCERT CA",
         "probe": "email",
-        "target-list": "Use your email address (edu preferred) as input",
         "certificate": "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"
     }
   ],