Add systemserverclasspath_fragment.

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

Bug: 180105615
Test: atest CtsClasspathsTestCases
Merged-In: I268e0fe441ef4935ba27d41205f6467632458eb3
Change-Id: I268e0fe441ef4935ba27d41205f6467632458eb3