Add bazel build for ui and junit.http, and the test packages.

A number of different test labels are supported:

  api
  attributes
  dfs
  diff
  http
  lfs
  lfs-server
  nls
  notes
  pack
  patch
  pgm
  reftree
  revplot
  revwalk
  storage
  submodule
  symlinks
  transport
  treewalk
  util

To run all tests:

  bazel test //...

To run specific tests, using labels:

  bazel test --test_tag_filters=api,dfs,revplot,treewalk //...

Change-Id: Ic41b05a79d855212e67b1b4707e9c6b4dc9ea70d
Signed-off-by: David Ostrovsky <david@ostrovsky.org>
Signed-off-by: Jonathan Nieder <jrn@google.com>

Only testonly targets (such as tests) need to use junit.

In particular this involves making the toplevel :all rule testonly.
It's not clear to me what that rule is for --- "bazel build //..."
already works to build all targets.  In any case it appears to be for
testing, so marking it as testonly shouldn't be harmful.

Change-Id: I28ff508ab8ce2ec0a0111109110aa9680d30600e

Test plan:

  $ bazel build all

  $ unzip -t bazel-genfiles/all.zip
    Archive:  bazel-genfiles/all.zip
      testing: libhttp-apache.jar       OK
      testing: libjgit-archive.jar      OK
      testing: libjgit-lfs-server.jar   OK
      testing: libjgit-lfs.jar          OK
      testing: libjgit-servlet.jar      OK
      testing: libjgit.jar              OK
      testing: libjunit.jar             OK
    No errors detected in compressed data of bazel-genfiles/all.zip.

Change-Id: I9e6c60898ccc6d2a4557ec7544c297442a9702b4
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Change-Id: I934114315d2c7cab917f1011b8e55c52367d429f
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

The initial implementation only builds the packages consumed by
Gerrit Code Review.

Test build and execution is not implemented.

We prefer to consume maven_jar custom rule from bazlets repository,
for the same reasons as in the Gerrit project:

* Caching artifacts across different clones and projects
* Exposing source classifiers and neverlink artifact

TEST PLAN:

  $ bazel build :all
  $ unzip -t bazel-genfiles/all.zip
  Archive: bazel-genfiles/all.zip
    testing: libjgit-archive.jar      OK
    testing: libjgit-servlet.jar      OK
    testing: libjgit.jar              OK
    testing: libjunit.jar             OK
  No errors detected in compressed data of bazel-genfiles/all.zip.

Change-Id: Ia837ce95d9829fe2515f37b7a04a71a4598672a0
Signed-off-by: David Ostrovsky <david@ostrovsky.org>
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>