create integration test framework

This is a basic integration test framework for kpatch, which tests
building, loading, and unloading patches, as well as any other related
custom tests.

The kpatch-test script looks for test input files in the
tests/integration directory.  It expects certain file naming
conventions:

- foo.patch - patch that should build successfully

- bar-FAIL.patch - patch that should fail to build

- foo-LOADED.test - executable which tests whether foo.patch module is
  loaded.  The kpatch-test script will use this executable to test that
  loading/unloading the patch module works as expected.

Any other *.test files will be executed after all the patch modules have
been built.