Continue process boot even if 'idmap2 --scan' fails

Relax the requirement on 'idmap2 --scan' to exit normally (as defined by
WIFEXITED) when starting a process. This allows the process to continue
booting, but with the caveat that no static="true" overlays targeting
"android" will be loaded.

The booting process is usually Zygote but can be an app that uses a
wrap.sh script (see https://d.android.com/ndk/guides/wrap-script).
Because SELinux rules prevent most processes from executing
/system/bin/idmap2, 'idmap2 --scan' will fail for "wrapped" apps.

Bug: 120854885
Test: atest CtsWrapWrapDebugTestCases CtsWrapWrapDebugMallocDebugTestCases
Change-Id: I85225cbcdd945f0026879e89f481d733217825d5