Test run work and results dir; relative path rules

[marshallward]

This patch consists of three changes to the test suite:

• Tests are now run in dedicated work directories. This allows for
  parallel execution of tests inside of make.

  Unexpected improvements are a 3-4x speedup on test time, and the
  disappearance of several anomalous "negative zero" issues which were
  otherwise unreproducible outside of the test, suggesting that
  replacing the serial runs inside of the tc directories has resolved
  some otherwise unknown problems.

• Makefile rules for running tests are now defined relative to the
  .testing directory, rather than an explicit base directory based on
  the path of the Makefile.

  Although this method is slightly less robust and slightly more prone
  to error, it makes it easier to build and run individual files within
  the project.

  Build paths are still absolute, and will be updated in a separate
  commit.

• Test output is now stored in a results directory, rather than inside
  the tc* configuration directories.

[codecov-io]

Codecov Report

Merging #1005 into dev/gfdl will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           dev/gfdl    #1005   +/-   ##
=========================================
  Coverage     43.16%   43.16%           
=========================================
  Files           213      213           
  Lines         62355    62355           
=========================================
  Hits          26918    26918           
  Misses        35437    35437

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[adcroft]

Looks good. I like the use of $* allowed by using the work dir patterns. make clean.stats is much cleaner.