Add building and installing of grep for vendor.

Merged from
https://android.googlesource.com/platform/system/core/+/0c3b1bd2a5354948845ac17a86d286f4cdd1f819 .

Bug: 38240024
Test: Verified that grep is installed in /vendor/bin.  See details in testing
done comment in https://googleplex-android-review.git.corp.google.com/2428550 .
Change-Id: I15e1f9994af90fc7edccf35adbbcef349aca6929