Move T0007_Index to exttst

This test depends upon the external git binary, and this isn't
really a pure Java test like our module tries to claim itself is.
So we move it out to exttst with other tests that require additional
external resources and/or executable code.

Change-Id: Ic9be0280c8bb50a5768336c64de794eb0a492b3d
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>