(maint) Remove vendor libraries in favor of find_package.

Removing Boost, log4cxx, and RE2 from the vendor directory. Instead, use
find_package to locate pre-existing binary packages.
(CFACT-8) Add unit test framework.

Adding gmock to vendor directory.
Building a test executable for libfacter.
Implementing, at first, unit test for string utility functions.
Adding tests to travis CI.
Merge pull request #24 from peterhuene/feature/testing

(CFACT-8) Add unit test framework.
(maint) Replace file utility functions with Boost file_system.

Adding Boost file_system to the build. This is a better cross-platform library for file system abstractions.
(CFACT-26) Add block device facts for Linux.

Implementing the following facts for Linux:

- blockdevice_<device>_size
- blockdevice_<device>_vendor
- blockdevice_<device>_model
- blockdevices