Fix the issue that makes GsiService::Cancel to block

The GsiService::Get shares the same mutex with other methods.
This makes the cancel method to block on the mutex.

Bug: 145891864
Test: open two terminals and execute commands below
  1st terminal gsi_tool install
  2nd terminal gsi_tool cancel

Change-Id: Ie458318013dfbbe11c831bf2eb0aa1132dceae30
1 file changed