included-tests: update gitian descriptors for hexdump dependency
included-tests: generate binary data from test files for inclusion into test binaries

This change moves test data into the binaries rather than reading them from
the disk at runtime.

Advantages:
- Tests become distributable
- Cross-compile friendly. Build on one machine and execute in an arbitrary
  location on another.
- Easier testing for backports. Users can verify that tests pass without having
  to track down corresponding test data.
- More trustworthy test results and easier quality assurance as tests make
  fewer assumptions about their environment.
- Tests could theoretically run at client/daemon startup and exit on failure.

Disadvantages:
- Required 'hexdump' build-dependency. This is a standard bsd tool that should
  be usable everywhere. It is likely already installed on all build-machines.
- Tests can no longer be fudged after build by altering test-data.
Merge pull request #2985 from theuni/included-tests

Embedded test data in bitcoin_test