In a local test, I observed virt-customize failing during ssh
key injection

Injecting ssh key to instack VM
[   0.0] Examining the guest ...
[  48.0] Setting a random seed
[  48.0] Running: mkdir /root/.ssh/
mkdir: cannot create directory '/root/.ssh/': File exists
virt-customize: mkdir /root/.ssh/: command exited with an error

Adding -p should prevent this from happening.

Change-Id: If8f085cba3083ccf3d5e8f648a9830f142ea53d9