testlib: Reduce lock holding time
testlib: Reduce lock holding time

Only lock the node_mgr for the shortest amount of time to prevent
things from stalling if we run into communication problems with
the node that is trying to connect.

Signed-off-by: Tony Asleson <1ef2d381aa56d512126ddaacc29e68136e4fdf55@redhat.com>

tasleson/lsm-ci,tasleson/lsm-ci