add a proper test scaffold and a small test suite

Add the Perl test scaffold module Test::ktap based on Test::Base, which
uses the IPC::Run3 module to automate the "ktap" program.

Detailed documentation has been added to file test/README.

v2:
    * added the "reindex" tool to automatically format the .t test
      files.
    * documented the "reindex" tool in test/README.
    * documented the "--- SKIP" feature in the test scaffold.

Signed-off-by: Yichun Zhang (agentzh) <agentzh@gmail.com>