Add libhwminijail for sandboxing with seccomp filters

This is a partial cherry-pick of the internal change, including just
libhwminijail. The user does not exist in AOSP yet.

Bug: 36453956
Test: mmma hardware/interface/minijail
Merged-In: Iab014ff357b7329085a5e18a92f51838d2c72371
Change-Id: I46b030efba25aac3c09cef9bfb782ecdc7187e70