Send REMOTE_BUGREPORT request to the SYSTEM user.

Remote bugreports are triggered from device owner apps which are on
user 0, to kee everything on the same user the bugreport generation
should be handled by user 0.

Test: manually tested remote bugreport flow in retail demo mode
Bug: 274543518
Change-Id: Ied7072e5cd82a0afda148951dcd9d01c2355d957