component/*/test-py2.cfg: extend stack/slapos-py2.cfg

With buildout3 all python2 software must extend this

component/nxdtest/test-py2.cfg

 # SlapOS software release to test nxdtest on Nexedi testing infrastructure.
 [buildout]
 extends =
-  ../defaults.cfg
   test.cfg
-
-[python]
-part = python2.7
-
-[openssl]
-<= openssl-1.1
+  ../../stack/slapos-py2.cfg

component/pygolang/test-py2.cfg

 # SlapOS software release to test pygolang/py2 on Nexedi testing infrastructure.
 
 [buildout]
-extends = test.cfg
-
-[python]
-part = python2.7
-
-[openssl]
-<= openssl-1.1
+extends =
+  test.cfg
+  ../../stack/slapos-py2.cfg

component/zodbtools/test-py2.cfg

-[python]
-part = python2.7
-
-[openssl]
-<= openssl-1.1
+[buildout]
+extends =
+  ../../stack/slapos-py2.cfg