Up until now, we have been using pexpect to spawn an lldb process and use lldb commands to

bring the debugger to the desired state.

This patch makes BenchBase inherit from TestBase, instead of Base (which is a parent class of
TestBase).  This is so that we can also enjoy the Pythonic way of bringing the lldb debugger
to a desired state before running the benchmark and collect statistics.

llvm-svn: 142562