CP-11163: Set a limit on the amount of data that is read by execute_ssh
CP-11163: Set a limit on the amount of data that is read by execute_ssh

Reading until the stream stops could allow malicious VMs to fill up Dom0's memory.

Signed-off-by: Rob Dobson <564e7c9301873eb0e5b6866dcaa1b131933d2ed5@citrix.com>

robertbreker/xscontainer,olivierlambert/xscontainer,xenserver/xscontainer,olivierlambert/xscontainer,robertbreker/xscontainer,xenserver/xscontainer