[baremetal] MaaS: Fix adding mcp.rsa.pub

[baremetal] MaaS: Fix adding mcp.rsa.pub

Upstream salt-formula-maas change [1] gated applying "maas_sshprefs"
low state by `region.sshprefs` being declared in reclass, which is
not true for our model.
Mend our region.sls patch to pass mcp.rsa.pub to MaaS unconditionally.
This fixes baremetal SSH login with mcp.rsa.

While at it, fix duplicate SSH key upload on MaaS state retry.

JIRA: FUEL-281

[1] https://github.com/salt-formulas/salt-formula-maas/commit/ec61dd6

Change-Id: I93941a689058f9f48f34861898fbe3ee6ce4e2b4
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit 9a96a6292f82411a00faf373ca180cb32c26061c)