* src/util/json.c, src/util/json.h: Declare returned strings
to be const
* src/qemu/qemu_monitor.c: Wire up JSON mode for qemuMonitorGetPtyPaths
* src/qemu/qemu_monitor_json.c, src/qemu/qemu_monitor_json.h: Fix
const correctness. Add missing error message in the function
qemuMonitorJSONGetAllPCIAddresses. Add implementation of the
qemuMonitorGetPtyPaths function calling 'query-chardev'.