Fix PipeTest_Streaming timeout
Fix PipeTest_Streaming timeout

Test was calling Size() inside read and write loops. Size()
makes 2 syscalls to return the pipe size, making the test
do a lot more work than it should.

PiperOrigin-RevId: 253824690

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor