Increase stack size for tests 1917 and 1934

Both these tests could fail under asan due to running out of stack
space. We increase the stacks of the secondary threads to 10 mb to
solve this problem.

This partially reverts 30f3e9ce.

Test: SANITIZE_HOST=address art/test/testrunner/testrunner.py -b --host --interp-ac -t 1934
Test: SANITIZE_HOST=address art/test/testrunner/testrunner.py -b --host --interp-ac -t 1917

Bug: 111837501
Bug: 112071036
Change-Id: I22450565c02d88cfbf584f67748eaa470b4920fc