Adds Hyper-V Compute Driver soft reboot implementation

Adds a soft reboot implementation for feature parity with other
Nova drivers as specified in the base virt driver's interface.

Co-Authored-By: Simona Iuliana Toader <itoader@cloudbasesolutions.com>

Change-Id: I963cbdacdfefca47d6e45fa0aafac188963bcaed
Implements: blueprint hyper-v-soft-reboot
Merge "Adds Hyper-V Compute Driver soft reboot implementation"