Reland "assemble_vintf: getFlagIfUnset harder errors"

This reverts commit 441fd2d532f0e26cdcb41aaacacfe45286eb98f1.

Reason for revert: reland the change that makes it a hard error.

Bug: 136042734
Bug: 116614862
Change-Id: I623856021a33abd4b97ff227831e74101be5d1f8
1 file changed