This is the basis of providing clean, unified exception handling to
piglit, this provides a set of Exception classes and a function
decorator to be used on main functions. Together these provide well
formatted error messages that differentiate between expected failures
and unexpected failures and provide clean, readable error messages.

The goal is that this will give us the ability to get clean errors when
they are expected, and the ability to hide stack traces when they're
not.

Stack traces for unexpected errors can be turned back on by setting the
PIGLIT_DEBUG environment variable

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>