Fix tests for Ant task "git-clone"

Fix tests for Ant task "git-clone"

If project.init() isn't called GitCloneTaskTest fails when started from
Eclipse, according to [1] calling init() is necessary to properly
initialize the Ant project programmatically.

Always set the destination folder in order to ensure that all test
resources are created under the project's target folder and do not
pollute the project's source tree with test data.

[1]
http://ant.1045680.n5.nabble.com/project-createTask-not-working-with-ant-1-8-2-td3385716.html

Change-Id: Icbeb62680b018a92673faa58828b5e850564c7a8
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>