Enable manual tests in CI:

Fixes: RIPD-1575. Fix argument passing to runner. Allow multiple unit
test selectors to be passed via --unittest argument. Add optional
integer priority value to test suite list. Fix several failing manual
tests. Update CLI usage message to make it clearer.

src/test/rpc/Book_test.cpp

@@ -1647,7 +1647,7 @@ public:
     }
 };
 
-BEAST_DEFINE_TESTSUITE(Book,app,ripple);
+BEAST_DEFINE_TESTSUITE_PRIO(Book,app,ripple,1);
 
 } // test
 } // ripple