Mynewt unit tests - Add repo prefix to dep lists.

The unit tests depend on a few Mynewt packages (`test/testutil` and
`sys/console/stub`).  If there is no repo prefix in the dependency
specifier, newt assumes the package is in the local repo (mcuboot)`.
This commit adds the `@apache-mynewt-core/` prefix to these
dependencies.

Signed-off-by: Christopher Collins <ccollins@apache.org>

boot/boot_serial/test/pkg.yml

@@ -24,7 +24,7 @@ pkg.keywords:
 
 pkg.deps:
     - "@mcuboot/boot/boot_serial"
-    - test/testutil
+    - "@apache-mynewt-core/test/testutil"
 
 pkg.deps.SELFTEST:
-    - sys/console/stub
+    - "@apache-mynewt-core/sys/console/stub"

boot/bootutil/test/pkg.yml

@@ -23,8 +23,8 @@ pkg.homepage: "http://mynewt.apache.org/"
 pkg.keywords:
 
 pkg.deps: 
-    - boot/bootutil
-    - test/testutil
+    - "@mcuboot/boot/bootutil"
+    - "@apache-mynewt-core/test/testutil"
 
 pkg.deps.SELFTEST:
-    - sys/console/stub
+    - "@apache-mynewt-core/sys/console/stub"