Incorrectly used moveToThread during shutdown

[ksuprynowicz]

This could lead to weird problems so will be worth investigating in the future:

[04/30 23:51:21] [WARNING] [default] QObject::moveToThread: Current thread (0x5572d2e4a9f0) is not the object's thread (0x5572d6b1a440).

[HifiExperiments]

maybe after #939 is merged we could audit the whole shutdown process. it’s always been finicky, especially script shutdown (although it’s been a lot better seemingly in the past few months due to all your great work)