Rename the init process inside PID namespaces.

Rename the init process that Minijail launches inside PID namespaces.
This makes it easier to identify things when looking at 'ps' output.

Bug: 30789126
Change-Id: Iffe3ea1fc2ecb66b1bae96912e2664913ca00d75
diff --git a/libminijail.c b/libminijail.c
index cb03d5e..0ba5f01 100644
--- a/libminijail.c
+++ b/libminijail.c
@@ -1538,7 +1538,7 @@
 	_exit(init_exitstatus);
 }
 
-int init(pid_t rootpid)
+void init(pid_t rootpid)
 {
 	pid_t pid;
 	int status;
@@ -2012,10 +2012,13 @@
 		 * WARNING above.
 		 */
 		child_pid = fork();
-		if (child_pid < 0)
+		if (child_pid < 0) {
 			_exit(child_pid);
-		else if (child_pid > 0)
-			init(child_pid);	/* never returns */
+		} else if (child_pid > 0) {
+			/* Best effort. Don't bother checking the return value. */
+			prctl(PR_SET_NAME, "minijail-init");
+			init(child_pid);	/* Never returns. */
+		}
 	}
 
 	/*