guest agent: add RPC blacklist command-line option

This adds a command-line option, -b/--blacklist, that accepts a
comma-seperated list of RPCs to disable, or prints a list of
available RPCs if passed "?".

In consequence this also adds general blacklisting and RPC listing
facilities to the new QMP dispatch/registry facilities, should the
QMP monitor ever have a need for such a thing.

Ideally, to avoid support/compatability issues in the future,
blacklisting guest agent functionality will be the exceptional
case, but we add the functionality here to handle guest administrators
with specific requirements.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qerror.c

@@ -64,6 +64,10 @@ static const QErrorStringTable qerror_table[] = {
         .error_fmt = QERR_COMMAND_NOT_FOUND,
         .desc      = "The command %(name) has not been found",
     },
+    {
+        .error_fmt = QERR_COMMAND_DISABLED,
+        .desc      = "The command %(name) has been disabled for this instance",
+    },
     {
         .error_fmt = QERR_DEVICE_ENCRYPTED,
         .desc      = "Device '%(device)' is encrypted",