tests: Support --config to enable tests to override config defaults

Implements a simple mechanism to allow tests to customize the
configuration.  For a given <name>-test.c just place a <name>.ini file
at the same location as the test itself.  Alternately, you can generate
a <name>.ini in the same directory that the compiled test is placed
(i.e. the top builddir).  If no configuration file is found, then no
configuration will be used (i.e. --no-config is specified.)

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-By: Derek Foreman <derekf@osg.samsung.com>
diff --git a/Makefile.am b/Makefile.am
index 2f16fac..543c736 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -967,7 +967,8 @@
 $(ivi_tests) : $(builddir)/tests/weston-ivi.ini
 
 AM_TESTS_ENVIRONMENT = \
-	abs_builddir='$(abs_builddir)'; export abs_builddir;
+	abs_builddir='$(abs_builddir)'; export abs_builddir; \
+	abs_top_srcdir='$(abs_top_srcdir)'; export abs_top_srcdir;
 
 TEST_EXTENSIONS = .la .weston
 LA_LOG_COMPILER = $(srcdir)/tests/weston-tests-env