HFX-1078: [SCTX-1635] Handle storage exception while unplugging VBD.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Merge pull request #1638 from siddharthv/HFX-1078

HFX-1078: [SCTX-1635] Handle storage exception while unplugging VBD.