Prepare for using requirements library.
Prepare for using requirements library.

openstack_requirements has a library now. To use it we need to do all
our reading of requirements after requirements is available.

Change-Id: I53f7a16b4b28d8234192ab1845e4a337ba7a8328

Tesora/tesora-project-config,dongwenjuan/project-config,anbangr/osci-project-config,openstack-infra/project-config,coolsvap/project-config,anbangr/osci-project-config,Tesora/tesora-project-config,openstack-infra/project-config,noorul/os-project-config,dongwenjuan/project-config,coolsvap/project-config,noorul/os-project-config