selftests/bpf: Improve by-name subtest selection logic in prog_tests

Improve subtest selection logic when using -t/-a/-d parameters.
In particular, more than one subtest can be specified or a
combination of tests / subtests.

-a send_signal -d send_signal/send_signal_nmi* - runs send_signal
test without nmi tests

-a send_signal/send_signal_nmi*,find_vma - runs two send_signal
subtests and find_vma test

-a 'send_signal*' -a find_vma -d send_signal/send_signal_nmi* -
runs 2 send_signal test and find_vma test. Disables two send_signal
nmi subtests

-t send_signal -t find_vma - runs two *send_signal* tests and one
*find_vma* test

This will allow us to have granular control over which subtests
to disable in the CI system instead of disabling whole tests.

Also, add new selftest to avoid possible regression when
changing prog_test test name selection logic.

Signed-off-by: Mykola Lysenko <mykolal@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220409001750.529930-1-mykolal@fb.com

tools/testing/selftests/bpf/testing_helpers.h

@@ -12,3 +12,11 @@ int bpf_test_load_program(enum bpf_prog_type type, const struct bpf_insn *insns,
 			  size_t insns_cnt, const char *license,
 			  __u32 kern_version, char *log_buf,
 			  size_t log_buf_sz);
+
+/*
+ * below function is exported for testing in prog_test test
+ */
+struct test_filter_set;
+int parse_test_list(const char *s,
+		    struct test_filter_set *test_set,
+		    bool is_glob_pattern);