selftests/ftrace: Make uprobe test more robust against binary name

Make add_remove_uprobe test case more robust against various real
binary name.
Current add_remove_uprobe.tc test expects the real binary of /bin/sh
is '*/bin/*sh', but it does not work on busybox environment.
Instead of using fixed pattern, use readlink to identify real binary
name.

Link: https://lore.kernel.org/r/173625187633.1383744.2840679071525852811.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc

@@ -6,8 +6,10 @@
 echo 0 > events/enable
 echo > dynamic_events
 
+REALBIN=`readlink -f /bin/sh`
+
 echo 'cat /proc/$$/maps' | /bin/sh | \
-	grep "r-xp .*/bin/.*sh$" | \
+	grep "r-xp .*${REALBIN}$" | \
 	awk '{printf "p:myevent %s:0x%s\n", $6,$3 }' >> uprobe_events
 
 grep -q myevent uprobe_events