Move wait_for_maxscale functionality inside MaxScale

By exposing a (currently undocumented) debug endpoint that lets one
monitor interval pass, we make the reuse of the monitor waiting
functionality a lot easier. With it, when MaxScale is started by the test
framework it knows that at least one monitor interval will have passed for
all monitors and that the system is ready to accept queries.

server/core/monitor.cc

@@ -20,6 +20,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <chrono>
 #include <string>
 #include <sstream>
 #include <set>
@@ -2487,6 +2488,34 @@ bool monitor_set_disk_space_threshold(MXS_MONITOR* monitor, const char* disk_spa
     return rv;
 }
 
+void monitor_debug_wait()
+{
+    using namespace std::chrono;
+    std::lock_guard<std::mutex> guard(monLock);
+    std::map<MXS_MONITOR*, uint64_t> ticks;
+
+    // Get tick values for all monitors
+    for (MXS_MONITOR* mon = allMonitors; mon; mon = mon->next)
+    {
+        ticks[mon] = mxb::atomic::load(&mon->ticks);
+    }
+
+    // Wait for all running monitors to advance at least one tick
+    for (MXS_MONITOR* mon = allMonitors; mon; mon = mon->next)
+    {
+        if (mon->state == MONITOR_STATE_RUNNING)
+        {
+            auto start = steady_clock::now();
+
+            while (ticks[mon] == mxb::atomic::load(&mon->ticks)
+                   && steady_clock::now() - start < seconds(60))
+            {
+                std::this_thread::sleep_for(milliseconds(100));
+            }
+        }
+    }
+}
+
 namespace maxscale
 {