eventconsumer: rework retry mechanism #273

the previous retry mechanism had a slight flaw: successful connections
did not reset the exponent on the retry interval. this results in
constantly growing retry intervals:

attempt #1 - wait 5s
attempt #2 - wait 10s
attempt #3 - success!
.
.
.
disconnect
attempt #4 - wait 20s

what we want to see however, is a pattern like so:

attempt #1 - wait 5s
attempt #2 - wait 10s
attempt #3 - success!
.
.
.
disconnect
attempt #1 - wait 5s

this is solved by slapping the retry logic around DialConnection, which
is a more atomic point of connection attempt. retry logic is also
offloaded to the github.com/avast-go/retry package

Signed-off-by: oppiliappan <me@oppi.li>