MXS-2243 System tests brings VMs by themselves (#193)

maxscale-system-test changed in order to control test environment by itself.
Every test checks which machines are running, compare with list of needed machines
and start new VMs is they are missing in the running machines list.
Tests are executiong MDBCI commands, MDBCI executable should be in the PATH

maxscale-system-test/execute_cmd.h

@@ -1,5 +1,4 @@
-#ifndef EXECUTE_CMD_H
-#define EXECUTE_CMD_H
+#pragma once
 
 #include <iostream>
 #include <unistd.h>
@@ -12,6 +11,4 @@ using namespace std;
  * @param res Pointer to variable that will contain command console output (stdout)
  * @return Process exit code
  */
-int execute_cmd(char* cmd, char** res);
-
-#endif      // EXECUTE_CMD_H
+int execute_cmd(char * cmd, char ** res);