tests: two single auxiliary scripts to run/generate wrapped tests

tests: two single auxiliary scripts to run/generate wrapped tests

* tests/config-shell-tests.sh, tests/parallel-tests.sh,
tests/gen-config-shell-tests, tests/gen-parallel-tests: Deleted,
their roles taken over by ...
* tests/wrap-tests.sh, tests/gen-wrap-tests: ... these new more
general scripts.
* tests/Makefile.am (EXTRA_DIST): Distribute the new scripts, and
do not distribute the obsolete ones anymore.
($(srcdir)/parallel-tests.am, $(srcdir)/config-shell-tests.am): Do
not include nor generate anymore, they have been superseded by ...
($(srcdir)/wrap-tests.am): ... this new fragment, automatically
generated by `gen-wrap-tests'.
(PTEST_LOG_COMPILER, SHTST_LOG_COMPILER): Delete, they are now
defined in the new `wrap-tests.am' makefile fragment.
(TEST_EXTENSIONS): Do not append to it anymore, that is now done
by the new `wrap-tests.am' makefile fragment above.
($(parallel_tests:.ptest=.log), $(config_shell_tests:.shtst=.log),
$(parallel_tests), $(config_shell_tests): Remove this dependencies,
superseded by ...
($(wrap_TESTS), $(wrap_LOGS)): ... these ones.
(MAINTAINERCLEANFILES): Delete, it's not used anymore.
(TESTS): Do not contain anymore `$(config_shell_tests)' nor
`$(parallel_tests)', contain `$(wrap_TESTS)' instead, as defined
by `$(srcdir)/wrap-tests.am'.
Other related minor edits and reorderings.
* bootstrap, tests/.gitignore, tests/README: Update.