Fix setup for ImportExportTests

Closing service tracker in test's setup method unbinds agent in
ImportExportImpl and is the cause of NPEs when calling
P2ImportExport's exportP2F(OutputStream, IInstallableUnit[], boolean,
IProgressMonitor).

Just open service tracker before test, keep it open during the test
and close it after the test.

Change-Id: I61c1f8d4b37e0b490d61f4b2496343e6f0132591
Signed-off-by: Mykola Nikishov <mn@mn.com.ua>
3 files changed