Enable build file sandboxing in fbandroid

Summary:
Enable build file sandboxing in fbandroid.
Importing modules in build files that are not whitelisted will be blocked, this can be overriden by using

  with allow_unsafe_import():
      import foo

`import os` and `import os.path` will not be blocked and will import a safe version of `os` module instead (functions not accessing the file system like `os.path.join()` will be accessible), full `os` module can be imported using `allow_unsafe_import()`

Reviewed By: plamenko

Differential Revision: D3649817

fbshipit-source-id: 3e6a3ab9c4c6a56a99ca7adf599323143a5844f4

lib/gtest/BUCK

@@ -5,9 +5,10 @@
 # LICENSE file in the root directory of this source tree. An additional grant
 # of patent rights can be found in the PATENTS file in the same directory.
 
-import os
-import urllib2
-import zipfile
+with allow_unsafe_import():
+    import os
+    import urllib2
+    import zipfile
 
 include_defs('//CSSLAYOUT_DEFS')