Add bootclasspath_fragment.

Note that the contents of the bootclasspath_fragment are added as
dependencies to an apex, so there is no need to duplicate them in
java_libs.

Bug: 180105615
Test: atest CtsClasspathsTestCases
Change-Id: Idf501d35b631782d6c0b6eed6f6063cfb332d8e6
1 file changed