Export commons:dbcp in gerrit-plugin-api

Some plugins depend on this library and for the bazel in-tree build to
work, it must be explicitly specified in the plugins dependencies. Given
this library is already present in gerrit-plugin-api, export it instead
so plugins do not have to specify it.

Change-Id: I79a36061b89ceb37c4a3017aad8abb89cdba8578
diff --git a/gerrit-plugin-api/BUILD b/gerrit-plugin-api/BUILD
index 2e768ee..067b4cd 100644
--- a/gerrit-plugin-api/BUILD
+++ b/gerrit-plugin-api/BUILD
@@ -20,6 +20,7 @@
     "//gerrit-gwtexpui:server",
     "//gerrit-reviewdb:server",
     "//gerrit-server/src/main/prolog:common",
+    "//lib/commons:dbcp",
     "//lib/commons:lang",
     "//lib/commons:lang3",
     "//lib/dropwizard:dropwizard-core",