test harness: "make -n check" works correctly with Solaris make

test harness: "make -n check" works correctly with Solaris make

To avoid some recipes being executed with "make -n", we used the
trick of issuing recursive make calls not directly with $(MAKE),
but with a simple indirection instead:
  ...
  am__stealth_MAKE = $(MAKE)
  ...
  target:
      ... $(am__stealth_MAKE) ...
  ...
This hack worked with GNU make, but, unfortunately, not with
Solaris make.  The present change removes the hack, and uses more
proper idioms to avoid unwanted recipe executions with "make -n".

Bug exposed by test case `parallel-tests-dry-run.test'.

* lib/am/check.am (am__stealth_MAKE): Remove, no more used.
(.log.trs): Break recipe in multiple shell invocations.
($(TEST_SUITE_LOG)): Likewise, and move some corner-case parts of
the recipe to ...
(am--redo-logs): ... this new internal helper .PHONY target.