Properly exclude hosttests/tools/tests directories

There was a typo that resulted in the ignored directory names being
concatenated rather than included individually in the list. This caused
us to unintentionally publish the "wrong" sources for all releases
since Mar 23, 2012.

Bug: 30798902
Change-Id: I51e3ad48c4487374fe5614d074c1c0f091d430e0
(cherry picked from commit 31dde68d9c361dbdbe9092918f8224da2471b576)