Bug 1085622 - Fix E10S_TESTING_ONLY define so that it only ever applies when E10S_TESTING_ONLY config is true. r=ally,glandium.

We were defining the E10S_TESTING_ONLY build-time define with the value of the E10S_TESTING_ONLY config variable,
regardless of the value of E10S_TESTING_ONLY. Even if E10S_TESTING_ONLY in configure was blank, we'd still define
E10S_TESTING_ONLY, which resulted in E10S_TESTING_ONLY ifdef'd code to be included when we didn't want it to.

We now only ever define E10S_TESTING_ONLY iff NIGHTLY_BUILD is defined, and we do it globally.

This also fixes a busted E10S_TESTING_ONLY ifdef that didn't have an endif.

--HG--
extra : amend_source : 9c8fe8db110765272fa666a5c118d388f87c23d7