http.test: Add missing plugin.properties to build

Change-Id: I17e2c22498092d25dace88319698626ce55df822
diff --git a/org.eclipse.jgit.http.test/build.properties b/org.eclipse.jgit.http.test/build.properties
index 54c9cd2..9ffa0ca 100644
--- a/org.eclipse.jgit.http.test/build.properties
+++ b/org.eclipse.jgit.http.test/build.properties
@@ -1,4 +1,5 @@
 source.. = tst/
 output.. = bin/
 bin.includes = META-INF/,\
-               .
+               .,\
+               plugin.properties