Fix checkmount  error parsing in swift-recon

- swift-recon now handles parsing instances where 'mounted' key (in unmounted
  and disk_usage) is an error message instead of a bool.
- Add's checkmount exception handling to the recon umounted endpoint.
- Updates existing unittest to have ismount throw an error.
- Updates unittests to cover the corner cases

Change-Id: Id51d14a8b98de69faaac84b2b34b7404b7df69e9
Merge "Fix checkmount  error parsing in swift-recon"