[gdb/testsuite] Fix gdb.server/multi-ui-errors.exp for remote target

Test-case gdb.server/multi-ui-errors.exp fails for target board
remote-gdbserver-on-localhost with REMOTE_TARGET_USERNAME=remote-target:
...
(gdb) PASS: gdb.server/multi-ui-errors.exp: interact with GDB's main UI
Executing on target: kill -9 6447    (timeout = 300)
builtin_spawn [open ...]^M
XYZ1ZYX
sh: line 0: kill: (6447) - Operation not permitted
...

The problem is that the kill command:
...
remote_exec target "kill -9 $gdbserver_pid"
...
intended to kill gdbserver instead tries to kill the ssh client session in
which the gdbserver runs, and fails because it's trying as the remote target
user (remote-target on localhost) to kill a pid owned by the the build user
($USER on localhost).

Fix this by getting the gdbserver pid using the ppid trick from
server-kill.exp.

Likewise in gdb.server/server-kill-python.exp.

Tested on x86_64-linux.

gdb/testsuite/gdb.server/multi-ui-errors.c

@@ -17,12 +17,17 @@
 
 #include <stdio.h>
 #include <unistd.h>
+#include <sys/types.h>
+
+pid_t server_pid;
 
 int
 main (void)
 {
   int i;
 
+  server_pid = getppid ();
+
   printf ("@@XX@@ Inferior Starting @@XX@@\n");
 
   for (i = 0; i < 120; ++i)

gdb/testsuite/gdb.server/multi-ui-errors.exp

@@ -100,6 +100,35 @@ with_spawn_id $gdb_main_spawn_id {
     gdb_test "echo hello\\n" "hello" "interact with GDB's main UI"
 }
 
+# Get the gdbserver PID.
+set gdbserver_pid 0
+with_spawn_id $gdb_main_spawn_id {
+    gdb_test "interrupt"
+
+    gdb_test_multiple "" "interrupt arrived" {
+	-re "Program received signal SIGINT, Interrupt\\.\r\n" {
+	    pass $gdb_test_name
+	}
+    }
+
+    gdb_test_multiple "p server_pid" "" {
+	-re -wrap " = ($decimal)" {
+	    set gdbserver_pid $expect_out(1,string)
+	    pass $gdb_test_name
+	}
+    }
+
+    gdb_test_multiple continue "" {
+	-re "Continuing\\.\r\n" {
+	    pass $gdb_test_name
+	}
+    }
+}
+
+if { $gdbserver_pid == 0 } {
+    return
+}
+
 # Now kill the gdbserver.
 remote_exec target "kill -9 $gdbserver_pid"
 

gdb/testsuite/gdb.server/server-kill-python.exp

@@ -30,12 +30,16 @@ if {[build_executable "failed to prepare" ${testfile} \
     return -1
 }
 
+set target_binfile [gdb_remote_download target $binfile]
+
 # Start gdbserver.
-set res [gdbserver_spawn "${binfile}"]
+set res [gdbserver_spawn "${target_binfile}"]
 set gdbserver_protocol [lindex $res 0]
 set gdbserver_gdbport [lindex $res 1]
 set gdbserver_pid [exp_pid -i $server_spawn_id]
 
+set break_linenr [gdb_get_line_number "@@XX@@ Inferior Starting @@XX@@"]
+
 # Generate a python script we will later source.
 set file1 [standard_output_file file1.py]
 set fd [open "$file1" w]
@@ -44,6 +48,9 @@ puts $fd \
 
 def do_gdb_stuff ():
     gdb.execute ('target $gdbserver_protocol $gdbserver_gdbport')
+    gdb.execute ('break $srcfile:$break_linenr')
+    gdb.execute ('continue')
+    gdb.execute ('p server_pid')
     gdb.execute ('continue')
 
 do_gdb_stuff()"
@@ -57,8 +64,22 @@ if {[gdb_spawn_with_cmdline_opts \
     return
 }
 
+# Get the gdbserver PID.
+set gdbserver_pid 0
+
 # Wait for the inferior to start up.
 with_spawn_id $server_spawn_id {
+    gdb_test_multiple "" "get gdbserver PID" {
+	-re " = ($decimal)\r\n" {
+	    set gdbserver_pid $expect_out(1,string)
+	    pass $gdb_test_name
+	}
+    }
+
+    if { $gdbserver_pid == 0 } {
+	return
+    }
+
     gdb_test_multiple "" "ensure inferior is running" {
 	-re "@@XX@@ Inferior Starting @@XX@@" {
 	    pass $gdb_test_name