Fix share memory collision in multi-communicator case.

Current SHM object name would only use pidHash and ranks as
identification, which would collide each other when program runs with
multiple communicators. Here we added commId info into pidHash, it makes
'pidHash'es of different communicators keeping in same process will be
distincted with each other.

src/include/utils.h

@@ -11,6 +11,7 @@
 #include <stdint.h>
 
 ncclResult_t getHostName(char* hostname, int maxlen);
+uint64_t getnHash(const char* string, int n);
 uint64_t getHostHash();
 uint64_t getPidHash();