[wp] testing syntax for provers

src/plugins/wp/tests/wp_tip/oracle/proof.res.oracle

+# frama-c -wp [...]
+[kernel] Parsing proof.i (no preprocessing)
+[wp] Running WP plugin...
+[wp] No proof obligations

src/plugins/wp/tests/wp_tip/proof.i

+/* run.config_qualif
+   DONTRUN:
+*/
+
+// Provers
+
+/*@
+  strategy P2: \prover(0.5);
+  strategy P1: \prover("alt-ergo");
+  strategy P3: \prover("cvc4","z3",3);
+ */