yanglint TEST tcltest package integration

The script for the 'except' tool actually uses the tcl language.
And the tcltest package can be used for unit testing. Tests for
yanglint in interactive mode and non-interactive mode can be quite
similar, so naturally tcl scripts can be used for non-interactive mode
testing as well. Because of this, testing using the shunit2 framework
has been removed.
diff --git a/tools/lint/tests/interactive/all.tcl b/tools/lint/tests/interactive/all.tcl
new file mode 100644
index 0000000..b22a5ab
--- /dev/null
+++ b/tools/lint/tests/interactive/all.tcl
@@ -0,0 +1,15 @@
+package require tcltest
+
+# Hook to determine if any of the tests failed.
+# Sets a global variable exitCode to 1 if any test fails otherwise it is set to 0.
+proc tcltest::cleanupTestsHook {} {
+    variable numTests
+    set ::exitCode [expr {$numTests(Failed) > 0}]
+}
+
+if {[info exists ::env(TESTS_DIR)]} {
+    tcltest::configure -testdir "$env(TESTS_DIR)/interactive"
+}
+
+tcltest::runAllTests
+exit $exitCode