Add compile time check that friendly AID names are < 32 characters

There is an internal buffer in bionic for user/group names that is 32
characters long including the trailing null, so we must restrict the
length of these names during compile time.

Bug: 27999086
Test: Successfully compile a valid config.fs
Test: Fail to compile a config.fs with AID name > 31 characters
Change-Id: I7fe887c630dd4d1033b86a5d8332480eb3b0fa07