Remove clang-3.8 which doesn't have a repository on apt.llvm.org any
more.

For OSX, xcode8.3 is explicitly specified.

/usr/local/Cellar is used as a cache repository to save brew install
time on OSX (and /usr/local was too big).

Debian autobake.sh is moved to a matrix include.

Other branches of the matrix build test other test suites.
An Ubuntu galera is downloaded and used in the test suite.

TYPE=RelWithDebInfo used with the test to provide backtraces with line
numbers when crashes occur.

Build of PLUGIN_AWS_KEY_MANAGEMENT enabled in build.

Code supporting TYPE=Debug and -DWITH_ASAN=ON included by not enabled
due to large numbers of errors.

Running more tests in parallel (6) as container based builds seem to
support them. The test case timeout has been set to 2 minutes as large
stalls will put test cases over 50 minute interval.

ccache enabled where possible. Linux clang builds don't use them as the
minimum CMake version isn't there.