Add hosts field for manifests

[#72389932]

Signed-off-by: Simon Leung <leungs@us.ibm.com>
allows multiple hosts(routes) to be created when app is pushed

[#72389932]

Signed-off-by: Simon Leung <leungs@us.ibm.com>
Allows both host and hosts in manifest

[finishes #72389932]

Signed-off-by: David Sabeti <dsabeti@pivotal.io>