Fix permissions on ironic virtual pm key

Private ssh keys should have permissions of 600. We also should
explicitly make this the case rather than relying on o-a-c to preserve
permissions from cloned code. Additionally, the ironic process needs to
be able to read this key.

Change-Id: I0f4ce9f0b641c8634a927f79a803159a8884aaf2
Merge "Fix permissions on ironic virtual pm key"