poke: rename -f/--force option to -u/--unsolicited

The old name will still be accepted for some time,
but will print a deprecation warning if used.

This commit also improves --help output.

Change-Id: I2ebac82423a5276109f4b40b382312bd852419de
diff --git a/tests/peek/ndnpoke.t.cpp b/tests/peek/ndnpoke.t.cpp
index 9bf51cf..621a699 100644
--- a/tests/peek/ndnpoke.t.cpp
+++ b/tests/peek/ndnpoke.t.cpp
@@ -180,10 +180,10 @@
   BOOST_CHECK_EQUAL(face.sentData.back().getSignature().getType(), tlv::DigestSha256);
 }
 
-BOOST_AUTO_TEST_CASE(ForceData)
+BOOST_AUTO_TEST_CASE(Unsolicited)
 {
   auto options = makeDefaultOptions();
-  options.wantForceData = true;
+  options.wantUnsolicited = true;
   initialize(options);
 
   poke->start();