libbinder_ndk_unit_test: shutdown wait time to 20s

Servicemanager will shut down a service after 10s, but this
appears to be hitting a race on certain devices. Switching to
20s to be safe. aidl_lazy_test is the main test testing these
APIs. This is just supposed to test the NDK APIs.

Bug: seeing in presubmit
Test: libbinder_ndk_unit_test
Change-Id: I71b18c917c739f41fffcca1f2250e450aa9d4703