Fix spurious undead process warning

Set the strict mode policy before Process.waitForProcessDeath.

Also eliminate some of the wtf warnings because we know it's
a legitimate case: a large process could get killed during
getProcessLocked(), and the caller would start a new process
right after that.

Bug: 161835160
Test: See b/161835160#comment3 for detailed test steps
Change-Id: I357b522943c88aa833dcf06013a9f8d2240c3967