Added multi-tracepoint benchmark using randomly generated tracepoints.
Now running benchmarks with varying online CPU count to measure scalability.
- Added the linux_cpu Python module to control the set of online CPUs on Linux.
- Changed benchmarks.py to vary the number of online CPUs when permitted.
Added a kernel benchmark.
- A new kernel module, lttng_benchmark, runs a loop with a simple
  tracepoint
- The benchmark is controlled using /sys/kernel/lttng_benchmark/
- The lttng_kernel_benchmark Python module provides a Python API to
  the kernel benchmarking module
- benchmarks.py runs the new benchmark using the Python module
Updated .gitignore to include new benchmarks and Python bytecode.
Fixed CPU range parsing in linux_cpu Python module.
Improved kernel benchmark to run one thread per online CPU.
Modified UST benchmarking tool to start one instance per online CPU.
Set the number of full passes to 5 and the number of fast passes to 100.