templates: update kselftest subset parameters

this commit changes variable names according
used in the linaro's test definitions.

Signed-off-by: Alexandra Pereira<alexandra.pereira@collabora.com>

Author: Alexandra

templates/kselftest/kselftest.jinja2

@@ -22,5 +22,5 @@
       parameters:
         TESTPROG_URL: {{ kselftests_url }}
         SKIPFILE: skipfile-lkft.yaml
-        KSELFTEST_COLLECTIONS: {{ kselftest_collections }}
-        KSELFTEST_TESTS: {{ kselftest_tests }}
+        TST_CMDFILES: {{ kselftest_collections }}
+        TST_CASENAME: {{ kselftest_tests }}