gems: update the bosh_vcloud_cpi gem to version 0.5.4

This version of the gem fixes additional cases not handled correctly
by the create_vm rollback code.
JSON-encode exception message for large messages

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Do not clean up VMs that were not bound

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>
Only promote trusty for AWS go-agent

Signed-off-by: Adam Stegman <astegman@pivotallabs.com>