Issue #25122: Fix test_eintr.test_open() on FreeBSD
Skip test_open() and test_os_open(): both tests uses a FIFO and signals, but
there is a bug in the FreeBSD kernel which blocks the test. Skip the tests
until the bug is fixed in FreeBSD kernel.
Remove also debug traces from test_eintr:
* stop using faulthandler to have a timeout
* remove print()
Write also open and close on two lines in test_open() and test_os_open()
tests. If these tests block again, we can know if the test is stuck at open or
close.
test_eintr: don't always run the test in debug mode.