issue #278: tests: fix fakessh.

See source comment. This behaviour always existed, but it now seems to
be triggered since we started draining the master side input buffer,
which someone was prolonging the life of the PTY.

tests/data/fakessh.py

@@ -3,6 +3,7 @@
 import optparse
 import os
 import shlex
+import subprocess
 import sys
 
 parser = optparse.OptionParser()
@@ -12,6 +13,11 @@ parser.disable_interspersed_args()
 
 opts, args = parser.parse_args(sys.argv[1:])
 args.pop(0)  # hostname
+
+# On Linux the TTY layer appears to begin tearing down a PTY after the last FD
+# for it is closed, causing SIGHUP to be sent to its foreground group. Since
+# the bootstrap overwrites the last such fd (stderr), we can't just exec it
+# directly, we must hold it open just like real SSH would. So use
+# subprocess.call() rather than os.execve() here.
 args = [''.join(shlex.split(s)) for s in args]
-print args
-os.execvp(args[0], args)
+sys.exit(subprocess.call(args))