Several test cases use common operations one files like existence checking, content comparing, etc. with the help of home-brew local helpers. The set makes use of some existing seastar:: ones and generalizes others into test/lib/. The primary intent here is `57 insertions(+), 135 deletions(-)`
Closes#13936
* github.com:scylladb/scylladb:
test: Generalize touch_file() into test_utils.*
test/database: Generalize file/dir touch and exists checks
test/sstables: Use seastar::file_exists() to check
test/sstables: Remove sstdesc
test/sstables: Use compare_files from utils/ in sstable_test
test/sstables: Use compare_files() from utils/ in sstable_3_x_test
test/util: Add compare_file() helpers
313ae4ddac