Close inherited PIPE before doing work

Gmake in Darwin has file descriptor leak.
In a full build, ota_from_target_files will inherits
more than 2000 open PIPEs from gmake and fails in a call to select.select().
This change fixes the build by closing the PIPEs before doing real work.

Change-Id: Ife021382198642a97bbbf0b623e4f24f3d86b2b2
diff --git a/tools/releasetools/ota_from_target_files b/tools/releasetools/ota_from_target_files
index aa691b4..cd10d7c 100755
--- a/tools/releasetools/ota_from_target_files
+++ b/tools/releasetools/ota_from_target_files
@@ -781,6 +781,7 @@
 
 if __name__ == '__main__':
   try:
+    common.CloseInheritedPipes()
     main(sys.argv[1:])
   except common.ExternalError, e:
     print