Fix usage of ProcessExecutionError exception

Commit https://github.com/stackforge/manila/commit/2d9a89a065ba7dbed9bb6ae1464a3b9ec99474a7
made changes to Manila, where it uses 'ssh_execute' function
from common code. But exception that is used was not changed.
So, set old exception as link to new one.

Change-Id: If266f07b4c93c50f59f09336b766ce8f8e415509
Closes-Bug: #1340684
Merge "Fix usage of ProcessExecutionError exception"