Zygote: Poll with timeout for pid

Do not use a blocking readInt. Poll for available bytes with a timeout.

(cherry picked from commit cbc42140)

Bug: 63638768
Test: m
Test: cts-tradefed run commandAndExit cts-dev -m CtsWrapWrapDebugTestCases
Change-Id: Ib2131c00aa47dd10bb940d8678bbbfb5a0346ad5