Allow including file_descriptor.h in fs_mgr. am: 5e6dfe3933 am: e44bd2ef37 am: d3338f3b86 am: 7c40c820f5

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1430218

Change-Id: I2b5ccfaa033f4ded363cbe453a29de8a2058f644