Use user specified ssh key when removing tmp key
Use user specified ssh key when removing tmp key

enable_ssh_admin was not using the user specified ssh key when removing
the generated tmp key. This could result in a permission denied error.

Change-Id: I3bd4ed6c58d6bffef811ee7ebc317056b34f2d3c
Closes-Bug: #1785704

openstack/python-tripleoclient