Use relative path for keystone-manage

To support package based installs, we shouldn't specify the full path to
keystone-manage anymore.

Depends on: Change-Id: I5f26faf4ac95f75e8e1f72b9a98c9309f4ed7324

Do not merge until the dependent change is committed.

Change-Id: I21c1e40558f2a2e798f7807c40ac9ac17a3a650d
Merge "Use relative path for keystone-manage"