Reduce file descriptor limit for 151-OpenFileLimit.

Under the assumption it is failing on host in some cases because it
takes too long to reach the limit. This change reduces the time it
takes to run the test from 50s down to 2s.

Test: time ./test/run-test --host --prebuild --interpreter --relocate --runtime-option -Xcheck:jni --64 151-OpenFileLimit
Bug: 32302133
Change-Id: I833e3a7aa2164a3cee2744f8e8c7e02365844aa0