Consume JGit from development tree: Add missing dependency
Consume JGit from development tree: Add missing dependency

To run the tests, hamcrest_library is needed for jgit project and
because of this issue: [1], bazel tries to resolve this external
dependency in gerrit project. Add hamcrest library to WORKSPACE file.

Test Plan:

* switch to using JGit from the development tree
* run the tests:

  bazel test --define jgit-dev=1 //...

[1] https://github.com/bazelbuild/bazel/issues/2391
Change-Id: I0fd16c26a6048aa1c852cf097cfca4ab230d0496

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