Paolo Bonzini authored Nov 27, 2018 and Philip Withnall committed Jan 18, 2019

The subprocess needs to access the test_log_fd.  If the file descriptors
are not left open, functions such as g_test_message may stomp on file
descriptors open by the subprocess and cause bad behavior of the test.

(Tweaked by Philip Withnall <bugzilla@tecnocode.co.uk> to fix review
comments.)