Fixes detach and ebs-instance terminate problems for DASManager and OverlayManager SCs

Removed the VmBootRecord entity upgrade code at Ken's request as well.

Refactored out TGT commands into new class called TGTWrapper and handles error codes
and error output consistently for all callers. Also added several testing classes
although they are currently mostly empty.

VolumeTokens and VolumeExportRecords now are updated correctly and automatically during
export/unexport operations. Delete requests will wait until a volume is unexported before
deletion proceeds (this is a case found in ebs-instance termination from running.)

Minor tweaks in storage/ebs_utils.c as well.