Add status reason for VNF

[bharaththiruveedula]

Request for Enhancement:

Currently tacker shows the status of the VNF like
+--------------------------------------+------+--------------+----------+----------------+
| id | name | description | mgmt_url | status |
+--------------------------------------+------+--------------+----------+----------------+
| d97300a1-2631-453e-818d-0e914e4805d9 | | demo-example | | DEAD |
+--------------------------------------+------+--------------+----------+----------------+

But the operators have no clue bout the status, unless they see the logs. So we need an extra information about the status.
For example
+--------------------------------------+------+--------------+----------+----------------+--------------------------+
| id | name | description | mgmt_url | status Status Reason |
+--------------------------------------+------+--------------+----------+----------------+
| d97300a1-2631-453e-818d-0e914e4805d9 | | demo-example | | PENDING_CREATE | Unable to reach VDU |
+--------------------------------------+------+--------------+----------+----------------+--------------------------+

It must also reflect in horizon.