Support subtest status 'FLAKY'

[Bryce Harrington]

FLAKY seems to be a valid status, as seen here:

https://autopkgtest.ubuntu.com/results/autopkgtest-kinetic/kinetic/arm64/r/rust-clang-sys/20220914_163137_7c4e6@/log.gz

autopkgtest [16:31:20]: test librust-clang-sys+libloading-dev:libloading: - - - - - - - - - - results - - - - - - - - - -
librust-clang-sys+libloading-dev:libloading FAIL non-zero exit status 101
autopkgtest [16:31:21]: @@@@@@@@@@@@@@@@@@@@ summary
rust-clang-sys:@ FLAKY non-zero exit status 101
librust-clang-sys-dev:clang_10_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_11_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_12_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_13_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_3_5 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_3_6 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_3_7 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_3_8 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_3_9 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_4_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_5_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_6_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_7_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_8_0 FAIL non-zero exit status 101
librust-clang-sys-dev:clang_9_0 FAIL non-zero exit status 101
librust-clang-sys-dev:default FAIL non-zero exit status 101
librust-clang-sys-dev:static FLAKY non-zero exit status 101
librust-clang-sys-dev: FAIL non-zero exit status 101
librust-clang-sys+libloading-dev:runtime PASS
librust-clang-sys+libloading-dev:libloading FAIL non-zero exit status 101

[Bryce Harrington (bryce)]

Fix Released in 0.6.0: https://launchpad.net/ppa-dev-tools/trunk/0.6