This change fixes Eclipse project generation when jgit is consumed from
external repository. Only path to the library is added, but not the
sourcepath.
Test Plan:
* Switch to using jgit from external repository by amending the path
in lib/jgit/jgit.bzl
* Run tools/eclipse/project.py
* Verify that classpath entries are added to the .classpath file
Change-Id: I2bdadb74b3ef869805a96671b7882917967998d6
596fff00cc