Add missing licensing headers for test classes

Commit and file info:
33817-p9 frameworks/base/core/tests/coretests/src/android/util/LogTest.java
39945-p9 frameworks/base/core/tests/coretests/src/android/text/SpannableTest.java
39945-p9 frameworks/base/core/tests/coretests/src/android/text/SpannableStringBuilderTest.java
39945-p9 frameworks/base/core/tests/coretests/src/android/text/SpannableStringTest.java

Change-Id: I1aac616069b7c26a00153d00118ced289d802e44