When nginx is started, it returns control before it has created its pid
file. Since this test suite relies on the existence of the pid file,
wait until the pid file exists before returning from nginx_start. Time
out after 2 seconds so that if there is a real problem starting nginx
we don't wait forever.
Fixes#144
This defines a skip() function in the tests preamble which can
be used to skip tests. Skipped tests are counted, and a reason
for them being skipped printed after running the tests.
This avoids potential issues when running the tests in environments which
might set variables which Nginx tries to read on startup. For example,
the $NGINX variable was being picked from the Travis-CI build matrix
configuration.
