Do not export package org.eclipse.jgit from jgit tests

Do not export package org.eclipse.jgit from jgit tests

Commit 3344b93c erroneously exported the package org.eclipse.jgit.lib
from the org.eclipse.jgit.test bundle which made this a split package
since the bundle org.eclipse.jgit exports the same package.

Split packages are evil in general and most probably caused the build
cycle errors observed recently when importing the jgit projects in
Eclipse [1].

[1] http://dev.eclipse.org/mhonarc/lists/jgit-dev/msg02012.html

Change-Id: I89919e56b928acdbff0b90e3919808025a8562c6
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>