xenapi: ensure pool based migrate is live

The current code is missing a flag to pool_migrate that should be
included to ensure the migrate is live. This change adds that flag to
both uses of VM.pool_migrate, namely the live-migrate call and the
host_maintenance call.

Fixes bug 1201795
Change-Id: I265baaba5e9bd9132bd5e1c6f9fb18cefab02cfb
Merge "xenapi: ensure pool based migrate is live"