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/misc/utils.cu

@@ -96,6 +96,15 @@ uint64_t getHash(const char* string) {
   return result;
 }
 
+uint64_t getnHash(const char* string, int n) {
+  // Based on DJB2, result = result * 33 + char
+  uint64_t result = 9527;
+  for (int c = 0; c < n; c++) {
+    result = ((result << 5) + result) + string[c];
+  }
+  return result;
+}
+
 /* Generate a hash of the unique identifying string for this host
  * that will be unique for both bare-metal and container instances
  * Equivalent of a hash of;