std::move member initializer lists

Was previously creating a weak_ptr from a shared_ptr that was already
moved. Only worked becuase the constructor wasn't actually moving the
argument as expected.
std::move in constructor initializer lists when desired.
Create the weak_ptr before moving.

Test: atest binderRpcTest
Bug: aosp/3212539 comment after submitting
Change-Id: I8ce98cbcb5e3a40b240ffb1114cbee41be976d61