runtime/cases/_ptest.py: rename it to ptest.py

It works now.

[YOCTO #11547]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

diff --git a/meta/lib/oeqa/runtime/cases/_ptest.py b/meta/lib/oeqa/runtime/cases/ptest.py
similarity index 100%
rename from meta/lib/oeqa/runtime/cases/_ptest.py
rename to meta/lib/oeqa/runtime/cases/ptest.py