cargo test used to be unreadable: subprocesses inherited the terminal, so
dpkg-buildpackage, apt and configure output interleaved with the harness
summary, and env_logger lines from parallel tests crossed each other.
New test_support module, compiled into test binaries only (inert stubs
otherwise) and initialized before main via .init_array:
- all log output goes to target/pkh-test-logs/<test>.log, one file per
test thread, so concurrent tests never interleave
- context-launched commands are captured line by line into the same file
(driver-level wrapper); test-code spawns use run_logged()
- a panic hook records failures and an atexit callback prints a matrix
(test name, panic location, message, log path) after the libtest
summary; tests panicking on purpose can opt out with a guard
Also fixes two test bugs found on the way:
- diff_checkbuilddeps_matrix compared dpkg-checkbuilddeps diagnostics
against English messages without pinning the locale
- run_source_build in differential tests now captures output like the
live-UI path does
vhaudiquet