Decrease the app zygote preload timeout.

We have received reports of apps in the field not completing their code
preload in reasonable amounts of time, which blocks other processes from
starting. Start timing out on zygote socket if preloading takes longer
than 15 seconds. Let's start conservative and bring this down over time.

Additionally, introduce a way to change the timeout through shell
commands; our tests for preloading code in the AppZygote can take a very
long time to complete, but are also difficult to split up.

Test: atest
android.seccomp.cts.SeccompHostJUnit4DeviceTest#testAppZygoteSyscalls
Bug: 263711574
Bug: 290874550
Bug: 362143834
Flag: EXEMPT bugfix

Change-Id: Ic80eca35734953a952fcb5814cac26c093204986