Fixed the "os subnet create", "os subnet list" and
"os subnet show" command output for host routes to
improve readability and to align with the "--host-route"
option on the "os subnet create" and "os subnet set"
commands.
Change-Id: Ida69ae1a0bdb2e1648f8b5c978fc80cf1bbe752f
Closes-Bug: #1572309