Fix active SSH connection restoration

Use a keyword teardown instead of a plain command to restore
the active SSH connection state. This prevents these keywords
from clobbering the active SSH connection when one of the
SSH commands fails.

Change-Id: I8001a4e4242df24c267e003dcdf7f24e7d6b4728
Signed-off-by: Jozef Behran <jbehran@cisco.com>