Some plugins, most notably owners-plugin, depend on prolog:common rule.
Given that this rule transitively depends on gerrit-server:server rule,
and this rule depends on virtually whole gerrit build graph, the final
plugin artifact contains effectively the whole gerrit war file content.
To fix that we expose prolog:common in plugin API. Moreover, adjust
prolog_cafe_library to not transitively depend on prolog runtime
library. We can do it, because gerrit-server already depends on it, so
that it's included in gerrit war anyway.
This change allows the owners-plugin to de-duplicate its size from 45 MB
to 1.5 MB only.
Change-Id: I8d7198a911c2da444c1822509988eda7d369af77
b9400254a6