zvariant: add ptest feature for zvariant test suite

zvariant: add ptest feature for zvariant test suite

Below is the output of run-ptest script under qemu

root@qemux86-64:~# /usr/lib/zvariant/ptest/run-ptest

running 37 tests
test framing_offset_size::tests::framing_offset_size_bump ... ok$<2>
test owned_value::tests::from_value ... ok$<2>
test object_path::unit::owned_from_reader ... ok$<2>
test str::tests::from_string ... ok$<2>
test signature::tests::signature_slicing ... ok$<2>
test str::tests::test_ordering ... ok$<2>
test owned_value::tests::map_conversion ... ok$<2>
test owned_value::tests::serde ... ok$<2>
test tests::enums ... ok$<2>
test tests::derive ... ok$<2>
test tests::f64_value ... ok$<2>
test tests::i16_value ... ok$<2>
test tests::fd_value ... ok$<2>
test tests::i32_value ... ok$<2>
test tests::i8_value ... ok$<2>
test tests::i64_value ... ok$<2>
test tests::ip_addr ... ok$<2>
test tests::issue_59 ... ok$<2>
test tests::issue_99 ... ok$<2>
test tests::array_value ... ok$<2>
test tests::object_path_value ... ok$<2>
test tests::dict_value ... ok$<2>
test tests::signature_value ... ok$<2>
test tests::serialized_size ... ok$<2>
test tests::struct_byte_array ... ok$<2>
test tests::struct_ref ... ok$<2>
test tests::str_value ... ok$<2>
test tests::option_value ... ok$<2>
test tests::struct_value ... ok$<2>
test tests::struct_with_hashmap ... ok$<2>
test tests::u16_value ... ok$<2>
test tests::u32_value ... ok$<2>
test tests::unit ... ok$<2>
test tests::u8_value ... ok$<2>
test tests::unit_fds ... ok$<2>
test tests::value_value ... ok$<2>
test tests::recursion_limits ... ok$<2>

test result: ok$<2>. 37 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.21s

root@qemux86-64:~#

Signed-off-by: Frederic Martinsons <frederic.martinsons@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>