deploy-cache: refresh authorized_keys from id_rsa

deploy-cache: refresh authorized_keys from id_rsa

When bootstrap cache is present, the cached id_rsa keypair is
copied to Fuel Master node after the initial packages are installed
(cobbler pp copies id_rsa.pub as /etc/cobbler/authorized_keys).

This leaves behind out-of-sync cobbler configuration, generated from
the fresh id_rsa.pub instead of the cached one.

While at it, also fix Fuel Master authorized_keys from ~/.ssh, which
is transferred via /etc/nailgun/settings.yaml to deployed nodes,
leading to nodes rejecting subsequent key-based ssh logins.

JIRA: ARMBAND-188
JIRA: ARMBAND-190

Change-Id: I58b45c9522b16c7d05dafcd1acaff4b8cc30013e
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>