bazel: abstract the build system in static serving.

Provide BazelBuild to stub out the Bazel build.

Tested:

Production use case:
1.) bazel build polygerrit && \
    $(bazel info output_base)/external/local_jdk/bin/java \
     -jar bazel-bin/polygerrit.war daemon -d ../test_site \
     --console-log --show-stack-trace

Development mode use cases:
2.) bazel build polygerrit \
      //polygerrit-ui:polygerrit_components.bower_components.zip &&
    $(bazel info output_base)/external/local_jdk/bin/java \
     -jar bazel-bin/polygerrit.war daemon \
     --polygerrit-dev -d ../gerrit_testsite --console-log --show-stack-trace

checked that updates under polygerrit-ui/app/index.html are served
live.

3.) Run tools/eclipse/project.py, started gwt_daemon launcher,
verified that it worked.

4.) Run tools/eclipse/project.py, started gerit_gwt_debug launcher,
verified that GWT SDM worked.

Change-Id: I9d105e00e953b63c78306e9e37d5152673627727
diff --git a/polygerrit-ui/BUILD b/polygerrit-ui/BUILD
index 4cc6899..0124f93 100644
--- a/polygerrit-ui/BUILD
+++ b/polygerrit-ui/BUILD
@@ -6,7 +6,7 @@
 load('//tools/bzl:genrule2.bzl', 'genrule2')
 
 bower_component_bundle(
-  name = "polygerrit_components",
+  name = "polygerrit_components.bower_components",
   deps = [
     '//lib/js:es6-promise',
     '//lib/js:fetch',