adjustment related with possible "invalidated" children in more platform operations

In particular, this should fix an error seen on the alpha logs where the resource client object was actually invalidated.

This fix could also probably help with the ongoing investigation with a instrument failing to initialize on alpha (with platform "Low Power JBox - RSN Bench Testing".

All the usual platform related tests that I run are passing successfully.

    bin/nosetests --with-processleak  --with-pycc --with-greenletleak \
    ion/agents/platform \
    ion/services/sa/observatory/test/test_platform_launch.py \
    ion/services/sa/observatory/test/test_platform_status.py