Preserve a format of RPC command definitions

Currently RPC commands are formatted in a way that it's easy to read
and that test/lint/check-rpc-mappings.py can parse it.

To void breaking test/lint/check-rpc-mappings.py script by running
clang-format, RPC command definitions should be disabled for clang-format.

src/rpc/client.cpp

@@ -18,6 +18,7 @@ public:
     std::string paramName;  //!< parameter name
 };
 
+// clang-format off
 /**
  * Specify a (method, idx, name) here if the argument is a non-string RPC
  * argument and needs to be converted from JSON.
@@ -174,6 +175,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "rescanblockchain", 1, "stop_height"},
     { "createwallet", 1, "disable_private_keys"},
 };
+// clang-format on
 
 class CRPCConvertTable
 {