tests: switch from t-lib.sh to init.sh

tests: switch from t-lib.sh to init.sh

* tests/init.cfg: Source t-local.sh.
* tests/t-local.sh: Replace trap so that we always run
scsi_debug_cleanup_, regardless of the cleanup_ function.
Replace each snippet like this:
-if test "$VERBOSE" = yes; then
-  set -x
-  parted --version
-fi
-
-: ${srcdir=.}
-. $srcdir/t-lib.sh
+. "${srcdir=.}/init.sh"; path_prepend_ ../parted

Use this command (LHS elided, because it was too long):
  git grep -l 'srcdir/t-lib.sh'|xargs perl -p0i -e \
    's!...!. "\${srcdir=.}/init.sh"; path_prepend_ ../parted\n!'

* tests/t3310-flags.sh: Adjust manually, since the snippet
didn't quite match.