Fix memory leak when used score2char()

As a result of performing valgrind in my environment, leak of score2char() was discovered.

```
==15978== 100 bytes in 10 blocks are definitely lost in loss record 117 of 211
==15978==    at 0x4A05FDE: malloc (vg_replace_malloc.c:236)
==15978==    by 0x35B8617AD0: score2char (in /usr/lib64/libcrmcommon.so.3.2.0)
==15978==    by 0x403C59: ??? (in /usr/libexec/pacemaker/stonithd)
==15978==    by 0x4038E4: ??? (in /usr/libexec/pacemaker/stonithd)
==15978==    by 0x403DD3: ??? (in /usr/libexec/pacemaker/stonithd)
==15978==    by 0x4057A8: ??? (in /usr/libexec/pacemaker/stonithd)                                                                                                                                               
==15978==    by 0x35B920A213: cib_native_notify (in /usr/lib64/libcib.so.3.0.1)
==15978==    by 0x39C703688B: g_list_foreach (in /lib64/libglib-2.0.so.0.2200.5)                                                                                                                                 
==15978==    by 0x35B921091B: ??? (in /usr/lib64/libcib.so.3.0.1)                                                                                                                                                
==15978==    by 0x35B862BD9F: ??? (in /usr/lib64/libcrmcommon.so.3.2.0)                                                                                                                                          
==15978==    by 0x39C7038F0D: g_main_context_dispatch (in /lib64/libglib-2.0.so.0.2200.5)
==15978==    by 0x39C703C937: ??? (in /lib64/libglib-2.0.so.0.2200.5)
==15978==    by 0x39C703CD54: g_main_loop_run (in /lib64/libglib-2.0.so.0.2200.5)
==15978==    by 0x4040C6: ??? (in /usr/libexec/pacemaker/stonithd)
==15978==    by 0x3A09E1ECDC: (below main) (in /lib64/libc-2.12.so)
==15978==                                                                                                                                                                                                        
{                                                                                                                                                                                                                
   <insert_a_suppression_name_here>
   Memcheck:Leak                                                                                                                                                                                                 
   fun:malloc                                                                                                                                                                                                    
   fun:score2char                                                                                                                                                                                                
   obj:/usr/libexec/pacemaker/stonithd
   obj:/usr/libexec/pacemaker/stonithd
   obj:/usr/libexec/pacemaker/stonithd                                                                                                                                                                           
   obj:/usr/libexec/pacemaker/stonithd                                                                                                                                                                           
   fun:cib_native_notify                                                                                                                                                                                         
   fun:g_list_foreach                                                                                                                                                                                            
   obj:/usr/lib64/libcib.so.3.0.1                                                                                                                                                                                
   obj:/usr/lib64/libcrmcommon.so.3.2.0                                                                                                                                                                          
   fun:g_main_context_dispatch                                                                                                                                                                                   
   obj:/lib64/libglib-2.0.so.0.2200.5                                                                                                                                                                            
   fun:g_main_loop_run                                                                                                                                                                                           
   obj:/usr/libexec/pacemaker/stonithd                                                                                                                                                                           
   fun:(below main)                                                                                                                                                                                              
}
```

Although it did not come out in valgrind, the potential thing which is carrying out the method of the similar call was also corrected.
pengine/master.c