Clean up use of pipe

Don't duplicate what's already in unique_fd.h
Also, code that tries to handle weird stdout condition won't work
because of cloexec; just don't try that.

My tests:
- Ensure Marlin device boots and vold_prepare_subdirs is called
successfully
- Try adb shell sm set-virtual-disk true, see that eg sgdisk output is
logged.

Bug: 26735063
Bug: 113796163
Test: details in commit
Change-Id: I5698ba0b4c8bd692a740a1bd445e677ad4815d11

Utils.cpp

@@ -297,29 +297,25 @@ status_t ForkExecvp(const std::vector<std::string>& args, std::vector<std::strin
                     security_context_t context) {
     auto argv = ConvertToArgv(args);
 
-    int fd[2];
-    if (pipe2(fd, O_CLOEXEC) != 0) {
-        PLOG(ERROR) << "pipe2 in ForkExecvp";
+    android::base::unique_fd pipe_read, pipe_write;
+    if (!android::base::Pipe(&pipe_read, &pipe_write)) {
+        PLOG(ERROR) << "Pipe in ForkExecvp";
         return -errno;
     }
-    android::base::unique_fd pipe_read(fd[0]);
-    android::base::unique_fd pipe_write(fd[1]);
 
     pid_t pid = fork();
     if (pid == 0) {
         if (context) {
             if (setexeccon(context)) {
-                LOG(ERROR) << "Failed to setexeccon";
+                LOG(ERROR) << "Failed to setexeccon in ForkExecvp";
                 abort();
             }
         }
         pipe_read.reset();
-        if (pipe_write.get() != STDOUT_FILENO) {
-            dup2(pipe_write.get(), STDOUT_FILENO);
-            pipe_write.reset();
-        }
+        dup2(pipe_write.get(), STDOUT_FILENO);
+        pipe_write.reset();
         execvp(argv[0], const_cast<char**>(argv.data()));
-        PLOG(ERROR) << "Failed to exec";
+        PLOG(ERROR) << "exec in ForkExecvp";
         _exit(EXIT_FAILURE);
     }
     if (pid == -1) {