Add subtest_id to _short_name_map_file for unfiltered test names

Stores the unfiltered short name as subtest_id in the existing
_short_name_map_file dictionary during cartesian config parsing,
preserving all subtest labels including type_specific and io-*
provider prefixes. Only applies to subtests.cfg variants.

Access via: params.get("_short_name_map_file")["subtest_id"]

Example:
 - subtest_id: "type_specific.io-github-autotest-qemu.
                guest_iommu_test.eim_off.default"

Assisted-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: Houqi (Nick) Zuo <hzuo@redhat.com>

Author: nickzhq

virttest/cartesian_config.py

@@ -139,9 +139,7 @@
 import re
 import sys
 
-_reserved_keys = set(
-    ("name", "shortname", "dep", "_short_name_map_file", "_name_map_file")
-)
+_reserved_keys = set(("name", "shortname", "dep", "_short_name_map_file", "_name_map_file"))
 options = None
 num_failed_cases = 5
 
@@ -1803,6 +1801,27 @@ def _parse(self, lexer, node=None, prev_indent=-1):
                         )
                         node3.content += [(lexer.filename, lexer.linenum, op)]
 
+                        # Store subtest_id in _short_name_map_file (only for subtests.cfg)
+                        if os.path.basename(lexer.filename) == "subtests.cfg":
+                            subtest_id_parts = []
+
+                            for label in node3.name:
+                                label_name = str(label.name)
+                                # Keep all parts without filtering
+                                subtest_id_parts.append(label_name)
+
+                            # Create the subtest_id map entry
+                            if subtest_id_parts:
+                                subtest_id_op = LUpdateFileMap()
+                                subtest_id_op.set_operands(
+                                    "subtest_id",
+                                    ".".join(subtest_id_parts),
+                                    "_short_name_map_file",
+                                )
+                                node3.content += [
+                                    (lexer.filename, lexer.linenum, subtest_id_op)
+                                ]
+
                         if node3.default and self.defaults:
                             # Move default variant in front of rest
                             # of all variants.