Add py.test to the list of tested pytest names

pytest is not being detected on OpenBSD 6.9:

checking for pytest-3... no
checking for py.test-3... no
checking for pytest... no
checking for pytest-pypy... no
configure: WARNING: pytest not found, some system tests will be skipped

It works for OpenBSD 6.8:

checking for pytest-3... no
checking for py.test-3... /usr/local/bin/py.test-3

It seems that pytest was renamed from py.test-3 to py.test. (This might be the change.)

The configure.ac check needs to be updated to detect py.test:

checking for pytest-3... no
checking for py.test... /usr/local/bin/py.test

This works:

diff --git a/configure.ac b/configure.ac
index 2518969534..9157c8bc01 100644
--- a/configure.ac
+++ b/configure.ac
@@ -303,7 +303,7 @@ AM_CONDITIONAL([HAVE_PERLMOD_TIME_HIRES],
 AM_PATH_PYTHON([3.4], [], [:])
 AM_CONDITIONAL([HAVE_PYTHON], [test "$PYTHON" != ":"])
 
-AC_PATH_PROGS([PYTEST], [pytest-3 py.test-3 pytest pytest-pypy], [])
+AC_PATH_PROGS([PYTEST], [pytest-3 py.test py.test-3 pytest pytest-pypy], [])
 AS_IF([test -z "$PYTEST"],
       [AC_MSG_WARN([pytest not found, some system tests will be skipped])])
 AC_SUBST([PYTEST])