lib: Partial Revert of 4ecc09d and modify zclient connect behavior

lib: Partial Revert of 4ecc09d and modify zclient connect behavior

Commit 43cc09d has been shown to cause several issues with clients
connecting.

Partial revert, since I wanted to keep the debug logs added
for that commit, as well remove the piece of code that
stops attempting to connect to zebra.  If we've failed
a bunch of times, there is nothing wrong with continuing
to do so once every 60 seconds.  I've debug guarded
the connect failure for those people running bgp
without zebra.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
Signed-off-by: Renato Westphal <renato@opensourcerouting.org>