Use java_import_external() for maven artifacts to allow usage of web proxy

Change-Id: I5c116ce33d35e51174b14c5022a5a9f183d01ecd
diff --git a/BUILD b/BUILD
index 6656a7a..18d867b 100644
--- a/BUILD
+++ b/BUILD
@@ -12,9 +12,9 @@
     visibility = ["//visibility:public"],
 )
 
-KARAF = "@apache_karaf//file"
+KARAF = "@apache_karaf//:apache_karaf"
 
-PATCHES = "@apache_karaf_patches//file"
+PATCHES = "@apache_karaf_patches//:apache_karaf_patches"
 
 BRANDING = "//tools/package/branding:onos-tools-package-branding"