Do not reuse non-leaf tasks for the starting activity

TV Settings activities were started in home stack because home stack
was originally created from TV Settings FallbackHome activity. So, it
was being reused for the Settings activities.

Only looks for the reused task from leaf tasks and also not setting
task affinity on non-leaf tasks.

Bug: 154517501
Test: start Settings activities and not landing on home stack
Change-Id: I07cb0e40248fd2a37f8e9cfe71d13651aed25207