[fuzz-utils] Add StringList (4/4: keep,erase_if)

This CL adds methods to StringList to keep or erase elements based
on a simple substring match.

SEC-103

Tests: Added more fuzz-utils unit tests.

Change-Id: I4fcf1eeb89c5c896a2d1e3e5a5bf20f34d687617

[fuzz-utils] Add StringList (3/4: clear)

This CL adds the clear method to StringList.

SEC-103

Tests: Added more fuzz-utils unit tests.
Change-Id: I9c7ba98a58b47539b1d133f7539d979b31ff17e8

[fuzz-utils] Add StringList (2/4: push_front,back)

This CL adds method to StringList to push C-style strings onto the
front or back of the list.

SEC-103

Tests: Added more fuzz-utils unit tests.

Change-Id: I849ff87c2479442e49e15bef1cc15f51fc1ea329

[fuzz-utils] Add StringList (1/4: basic getters)

This CL introduces the fuzz-utils library, which provides code for the
command line fuzzing tool. As an initial commit, it adds a small
helper class for managing C-style strings in a fbl::DoublyLinkedList.

SEC-103

Tests: Added fuzz-utils unit tests.

Change-Id: Iaac788d412bfab1e573188a413cc3841d983f7b1