test: Initial testing framework

Configure with --enable-testtools.

BLD_ROOT is now the top build directory.

Current test requires ttynvt to be started (by root) like
 # BLD_ROOT/src/ttynvt -d -E -S localhost:1234 -n ttyNVT99
Device and server name parameters must be as shown above.

Run tests like
 $ make -C BLD_ROOT test 	# Builds the other programs too
 $ make -C BLD_ROOT/test	# Only running tests
 $ make -C BLD_ROOT/test V=1 RUN_OPTS="--gtest_filter=Test1.t1"

Makefile.am

@@ -9,3 +9,11 @@ if BUILD_TESTTOOLS
 SUBDIRS += nvtsrv
 SUBDIRS += nvttest
 endif
+if BUILD_TEST
+SUBDIRS += test
+endif
+
+.PHONY: $(SUBDIRS) test
+$(SUBDIRS) test:
+	$(MAKE) -C $@
+test: $(SUBDIRS)