libsnapshot: Detach the daemon explicitly before stopping the service

If the daemon is alive, detach it before explicitly terminating service.

Bug: 316876960
Test: treehugger presubmit tests
Change-Id: I94d9d1a0dab09a6b016f422c7497098abc86add8
Signed-off-by: Akilesh Kailash <akailash@google.com>