Mynewt: Partial fix for bootutil unit test

The bootutil unit tests fail to build with the following error:

    Testing package @mcuboot/boot/bootutil/test
    Unsatisfied APIs detected:
        * log, required by: sys/log/modlog

This commit adds a `sys/log/stub` dependency to the bootutil unit test
package.

NOTE: This unit test package still fails to build because the code is
out of date.  This commit just fixes one of several issues.

Signed-off-by: Christopher Collins <ccollins@apache.org>
diff --git a/boot/bootutil/test/pkg.yml b/boot/bootutil/test/pkg.yml
index 5da5fd7..74da525 100644
--- a/boot/bootutil/test/pkg.yml
+++ b/boot/bootutil/test/pkg.yml
@@ -28,3 +28,4 @@
 
 pkg.deps.SELFTEST:
     - "@apache-mynewt-core/sys/console/stub"
+    - "@apache-mynewt-core/sys/log/stub"