selftests: ublk: install test_common.sh and trace/ scripts

Every ublk test script sources test_common.sh from its own directory:

    . "$(cd "$(dirname "$0")" && pwd)"/test_common.sh

and test_generic_02/12 additionally run bpftrace against the scripts in
trace/. Neither test_common.sh nor trace/ is listed in TEST_FILES, so
"make install" does not copy them into the install directory and every
ublk test fails when run from there:

  ./test_generic_02.sh: line 4: .../kselftest_install/ublk/test_common.sh: No such file or directory
  ./test_generic_02.sh: line 8: _have_program: command not found

The bpftrace tests are affected even when bpftrace is installed: the
missing trace/*.bt makes bpftrace exit immediately, and the tests then
report a skip rather than a failure, which hides the problem.

Add both to TEST_FILES, matching how other selftests ship their sourced
helpers (see kexec/kexec_common_lib.sh and zram/zram_lib.sh).

Fixes: 6aecda00b7 ("selftests: ublk: add kernel selftests for ublk")
Fixes: 723977cab4 ("selftests: ublk: add generic_01 for verifying sequential IO order")
Cc: stable@vger.kernel.org # v6.15+
Assisted-by: Kiro:claude-opus-5
Signed-off-by: Mahmoud Nagy Adam <mngyadam@amazon.de>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260909132602.68852-2-mngyadam@amazon.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/testing/selftests/ublk/Makefile

@@ -73,6 +73,8 @@ TEST_PROGS += test_stress_08.sh
 TEST_PROGS += test_stress_09.sh
 
 TEST_FILES := settings
+TEST_FILES += test_common.sh
+TEST_FILES += trace
 
 TEST_GEN_PROGS_EXTENDED = kublk metadata_size
 STANDALONE_UTILS := metadata_size.c