Add an error check for ReleaseTarball#create_from_unpacked.
Add an error check for ReleaseTarball#create_from_unpacked.

The hope is that this flaky test will error with better messaging.

[#93931010]

Signed-off-by: Corey Innis <c6de6a297c7ba72017894924528d266f693d3f31@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh