libutils: Fix integer overflows in VectorImpl.

Use external/safe-iop to check for overflows on arithmetic
operations.

Also remove an unnecessary copy of Vector/SharedBuffer from
codeflinger and use the copy from libutils instead.

Note that some of the unit tests are somewhat useless due to
test-runner limitations : gtest's ability to filter on abort message
doesn't work when combined with messages formatted by android's logging
system.

bug: 22953624

Change-Id: I46b1ae8ca1f3a010be13aca36a091e76a97a7b70