These were some issues flushed out when trying to run the Python performance benchmarks.

Changes:

• Add a tests to run one of the Python perf benchmark functions as part of the test suite.
• Stub a load of networking syscalls that are called the old-school way by some of the dynamically linked libraries (specifically subprocess).
• Implement waitpid (also called by subprocess).
• Update to latest cpp and python clients.
• Update Faasm version.

Note that this build introduces a new version of Faasm, which picks up the latest version of our WAVM fork. This now includes includes this commit: faasm/WAVM@81225ec , which should solve the sporadic stack allocation issues we're seeing in tests at the moment.