coroutine: add test-coroutine automated tests

To run automated tests for coroutines:

  make test-coroutine
  ./test-coroutine

On success the program terminates with exit status 0.  On failure an
error message is written to stderr and the program exits with exit
status 1.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

.gitignore

@@ -36,6 +36,7 @@ qemu-io
 qemu-ga
 qemu-monitor.texi
 QMP/qmp-commands.txt
+test-coroutine
 .gdbinit
 *.a
 *.aux