Add --cleanup to instance failover manpage
Add --cleanup to instance failover manpage

Describe the new parameter in the manpage of gnt-instance.

Signed-off-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

dimara/ganeti,leshchevds/ganeti,yiannist/ganeti,dimara/ganeti,apyrgio/ganeti,ganeti/ganeti,ganeti/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,leshchevds/ganeti,mbakke/ganeti,onponomarev/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,yiannist/ganeti,leshchevds/ganeti,andir/ganeti,andir/ganeti,grnet/snf-ganeti,mbakke/ganeti,apyrgio/ganeti,ganeti/ganeti,bitemyapp/ganeti,andir/ganeti,ganeti-github-testing/ganeti-test-1