init: increase thermal shutdown timeout to 3s

1) increase thermal shutdown timeout to 3s for process to save work
2) respect property "ro.build.shutdown_timeout" in thermal shutdown if
   it is set less than default time - "3s"

Bug: 112432890
Test: Build
Change-Id: Idc2b24dd44c1fab8f9b047fd2468de2ee45ff783
Merged-In: Idc2b24dd44c1fab8f9b047fd2468de2ee45ff783
(cherry picked from commit b5de0882)