Add support for running 3.x under ThreadSanitizer via CV jobs

We want to be able to run the C/C++ components of 3.x under ThreadSanitizer, to detect threading issues. This should be done during commit-validation, similar to the watson/master commit-validation jobs (e.g. http://cv.jenkins.couchbase.com/job/ep-engine-threadsanitizer-master/)

Approach

A pretty straightforward way to achieve this is to enable the building of rel-3.0.x.xml on the current watson build slaves (ubuntu12.04-cv), as these already have all the Clang-related tooling for ThreadSanitizer. (That is opposed to modifying the 3.x builders to add Clang/ThreadSanitizer). Afiak there's two main things needed to achieve this:

1. Backport our CMake changes to enable and configure building with ThreadSanitzer - see MB-15435.
2. Optionally allow the use of the sherlock/watson pre-packaged 3rd party dependancies (cbdeps); as the ubuntu12-cv images do /not/ already have the various 3rd party dependancies which 3.x normally uses installed.