adb: setsid() for adb host server.

To create a daemon for adb host server, we should call setsid()
for the daemon process. However, previously we call setsid() for
the adb client process, which results in nothing but EPERM error.

Bug: 26982628
Change-Id: I2763ae3d5a243706927d7ef6af5095138c0ce2d8
(cherry picked from commit 6bf323b97a)

adb/adb.cpp

@@ -883,8 +883,6 @@ int launch_server(int server_port)
             fprintf(stderr, "ADB server didn't ACK\n" );
             return -1;
         }
-
-        setsid();
     }
 #endif /* !defined(_WIN32) */
     return 0;

adb/client/main.cpp

@@ -127,10 +127,12 @@ int adb_server_main(int is_daemon, int server_port, int ack_reply_fd) {
         setup_daemon_logging();
 
 #if !defined(_WIN32)
-        // Set the process group so that ctrl-c in the spawning process doesn't kill us.
-        // Do this here instead of after the fork so that a ctrl-c between the "starting server" and
-        // "done starting server" messages gets a chance to terminate the server.
-        setpgrp();
+        // Start a new session for the daemon. Do this here instead of after the fork so
+        // that a ctrl-c between the "starting server" and "done starting server" messages
+        // gets a chance to terminate the server.
+        if (setsid() == -1) {
+            fatal("setsid() failed: %s", strerror(errno));
+        }
 #endif
 
         // Any error output written to stderr now goes to adb.log. We could