Convert rescue v3 plugin to v2.1 API

Changes required to have v3 plugin natively support the V2.1
API.

The parameters admin_password and image_ref were reverted to
adminPass and rescue_image_ref

Partially implements blueprint v2-on-v3-api
Co-Authored-By: Chris Yeoh <cyeoh@au1.ibm.com>
Change-Id: Ibca991b5d6ec065ea9fbb0318c4ab51a3c5a3eba
Merge "Convert rescue v3 plugin to v2.1 API"