Add {assert,expect}_command to unittest

The new assert_command and expect_commad functions of unittest allow for
executing a command and validating any combination of its exit code, stdout
and stderr.

These new functions are added to an auxiliary module within the private
unittest subdirectory because their implementation is huge.
Add equal and not_equal check operators

This adds new assert_equal, expect_equal, assert_not_equal and
expect_not_equal tests to the unittest library.
Convert base_test to unittest
Convert bool_test to unittest
Convert cleanup_test to unittest
Convert cli_test to unittest
Convert config_test to unittest
Convert cvs_test to unittest
Convert list_test to unittest

While doing this, fix the filter function to output the filtered results
as a single line instead of multiple lines.  Allows for equality comparison
of the results.
Convert process_test to unittest
Convert shtk_test to unittest
Convert version_test to unittest
Stop using ATF in favor of our unittest module

All of our test programs have been converted to our own unittest module
so we need not use atf-sh any longer.  Remove all mentions of ATF.