Issue with scala_specs2_unit_test + --strict_java_deps=ERROR

Hi everyone!

When I build some of our `scala_specs2_junit_test` targets using `--strict_java_deps=ERROR`, I get errors that I'm not sure how to resolve.

```
error: Target 'Unknown label of file bazel-out/local-fastbuild/genfiles/external/scala/_ijar/scala-parser-combinators/external/scala/lib/scala-parser-combinators_2.11-1.0.4-ijar.jar which came from @io_bazel_rules_scala//specs2:specs2' is used but isn't explicitly declared, please add it to the deps.
You can use the following buildozer command:
buildozer 'add deps Unknown label of file bazel-out/local-fastbuild/genfiles/external/scala/_ijar/scala-parser-combinators/external/scala/lib/scala-parser-combinators_2.11-1.0.4-ijar.jar which came from @io_bazel_rules_scala//specs2:specs2' //util:test

error: Target 'Unknown label of file bazel-out/local-fastbuild/genfiles/external/scala/_ijar/scala-xml/external/scala/lib/scala-xml_2.11-1.0.5-ijar.jar which came from @io_bazel_rules_scala//specs2:specs2' is used but isn't explicitly declared, please add it to the deps.
You can use the following buildozer command:
buildozer 'add deps Unknown label of file bazel-out/local-fastbuild/genfiles/external/scala/_ijar/scala-xml/external/scala/lib/scala-xml_2.11-1.0.5-ijar.jar which came from @io_bazel_rules_scala//specs2:specs2' //util:test
two errors found
two errors found
```

Normally I would add the jar to the deps list, but I'm not sure how to do that here. Both scala-parser-combinators and scala-xml are `maven_jar`s in my `WORKSPACE` file. I've added them to the `deps` list for the test target, but it doesn't seem to change anything.

If there's a bug, I'm happy to provide debug info and fix it. If this is an issue with my ignorance of bazel, then I'm happy to update docs somewhere to help others avoid this in the future.

Here are the rules from the `BUILD` file

```
shared_deps = [
"//a",
"//b",
"//c",
"//d",
"@com_typesafe_scala_logging_scala_logging_2_11//jar:file",
"@com_fasterxml_jackson_core_jackson_annotations//jar",
"@com_fasterxml_jackson_core_jackson_core//jar",
"@com_fasterxml_jackson_core_jackson_databind//jar",
"@com_typesafe_config//jar",
"@com_typesafe_play_play_datacommons_2_11//jar",
"@com_typesafe_play_play_functional_2_11//jar",
"@com_typesafe_play_play_iteratees_2_11//jar",
"@com_typesafe_play_play_json_2_11//jar",
"@commons_io_commons_io//jar",
"@joda_time_joda_time//jar",
"@org_apache_httpcomponents_httpclient//jar",
"@org_apache_httpcomponents_httpcore//jar",
"@org_apache_httpcomponents_httpmime//jar",
"@org_scala_lang_modules_scala_parser_combinators_2_11//jar",
"@org_scala_lang_modules_scala_xml_2_11//jar",
"@org_scala_lang_plugins_scala_continuations_library_2_11//jar",
"@org_slf4j_slf4j_api//jar",
]

scala_macro_library(
name = "util",
srcs = glob(["src/main/**/*.scala"]) + glob(["src/main/**/*.java"]),
resources = glob(["src/main/resources/**"]),
visibility = ["//visibility:public"],
deps = shared_deps + [
"//e",
"//f",
"//g",
"//e",
"@com_amazonaws_aws_java_sdk_core//jar",
"@com_amazonaws_aws_java_sdk_sts//jar",
"@com_github_nscala_time_nscala_time_2_11//jar",
"@com_lucidchart_thread_context//jar",
"@commons_codec_commons_codec//jar",
"@net_sf_ehcache_ehcache_core//jar",
"@org_apache_httpcomponents_httpasyncclient//jar",
"@org_scala_lang_modules_scala_java8_compat_2_11//jar",
"@org_scalaz_scalaz_core_2_11//jar:file",
]
)

scala_specs2_junit_test(
name = "test",
srcs = glob(["src/test/**/*.scala"]),
resources = glob(["src/test/resources/**"]),
deps = shared_deps + [
":util",
"@junit_junit//jar",
"@org_mockito_mockito_core//jar",
"@org_objenesis_objenesis//jar",
"@org_specs2_specs2_mock_2_11//jar",
],
suffixes = ["Spec", "Test"],
timeout = "short",
print_discovered_classes = True,
)
```

Start with the WORKSPACE maven_jar declarations and the BUILD file's shared_deps, util, and test rules. Reproduce the scala_specs2_junit_test build with --strict_java_deps=ERROR, then trace why the specs2 dependencies are not recognized; done means the target builds without the reported undeclared scala-parser-combinators and scala-xml errors.

Written by the indexing model from the issue text.