Tests that require PRNG are by default seeded from `/dev/urandom`.
However, the user should be able to override with a given seed
to reproduce a failing test.
Instead of messing with command-line arguments, a cleaner approach
is to fetch the seed from an environment variable.
For `ATX_CHECK_FS()` and `ATX_CHECK_FS_NEW()`, do not skip the test
if a backend (or its "-write" feature) is disabled, since
`exit 77` skips the entire test group, not current `AT_CHECK()`.
Instead, silently pass the current test.
- Move common defs and helper functions to check_util.h/check_utils.c.
- Add a prepare script argument for ATX_CHECK_FS* macros.
- ASSERT_EXPR_INT(): Use long int as expression result type.
- Other misc updates.
- Do not exit with status 99. It is considered a "hard failure"
in Autotest, and cleanup script won't be executed.
- Fix ATX_FEAT_PREREQ().
- Remove unneeded helper macros.
- Add more log output.
This is meant to be a workaround for a limitation of Autotest,
where `set -e` has no effect in AT_CHECK().
Also we don't want to use `trap ... ERR`, since it is not portable.
