Floss: Increase the manager timeout to 15 seconds

If btmanagerd start timeout is shorter than stack start timeout, it is
possible that the stack is still initializing but btmanagerd terminates
the process because of timeout. This could also cause crash because no
gurantee to the order of freeing memory.

Bug: 374017641
Bug: 304997914
Tag: #floss
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT, Floss-only changes
Change-Id: I40daf5a05a81783ef381ceaa9c42db8e77f59a28