lava: Support sharding for LTP

Some of the LTP suites (especially the syscalls suite) are extremely
large and take a very long time to run, in order to make jobs more
managable the test-definitions integration for LTP supports sharding
the suites.  Add support for this to our template.

Signed-off-by: Mark Brown <[email protected]>

Author: broonie

config/runtime/tests/ltp.jinja2

@@ -12,3 +12,5 @@
             TST_CMDFILES: "{{ tst_cmdfiles|default('') }}"
             SKIP_INSTALL: "{{ skip_install }}"
             SKIPFILE: {{ skipfile }}
+            SHARD_NUMBER: {{ shard_number|default(1) }}
+            SHARD_INDEX: {{ shard_index|default(1) }}