Add ability to specify a list of test name substrings for selecting which
tests to run. So now -t is accepting a comma-separated list of strings,
similarly to how -n accepts a comma-separated list of test numbers.

Additionally, add ability to blacklist tests by name. Blacklist takes
precedence over whitelist. Blacklisting is important for cases where it's
known that some tests can't pass (e.g., due to perf hardware events that are
not available within VM). This is going to be used for libbpf testing in
Travis CI in its Github repo.

Example runs with just whitelist and whitelist + blacklist:

  $ sudo ./test_progs -tattach,core/existence
  #1 attach_probe:OK
  #6 cgroup_attach_autodetach:OK
  #7 cgroup_attach_multi:OK
  #8 cgroup_attach_override:OK
  #9 core_extern:OK
  #10/44 existence:OK
  #10/45 existence___minimal:OK
  #10/46 existence__err_int_sz:OK
  #10/47 existence__err_int_type:OK
  #10/48 existence__err_int_kind:OK
  #10/49 existence__err_arr_kind:OK
  #10/50 existence__err_arr_value_type:OK
  #10/51 existence__err_struct_type:OK
  #10 core_reloc:OK
  #19 flow_dissector_reattach:OK
  #60 tp_attach_query:OK
  Summary: 8/8 PASSED, 0 SKIPPED, 0 FAILED

  $ sudo ./test_progs -tattach,core/existence -bcgroup,flow/arr
  #1 attach_probe:OK
  #9 core_extern:OK
  #10/44 existence:OK
  #10/45 existence___minimal:OK
  #10/46 existence__err_int_sz:OK
  #10/47 existence__err_int_type:OK
  #10/48 existence__err_int_kind:OK
  #10/51 existence__err_struct_type:OK
  #10 core_reloc:OK
  #60 tp_attach_query:OK
  Summary: 4/6 PASSED, 0 SKIPPED, 0 FAILED
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Cc: Julia Kartseva <hex@fb.com>
Link: https://lore.kernel.org/bpf/20200116005549.3644118-1-andriin@fb.com