SNMP timeout and retries are now configurable through ironic.conf. This
allows to have custom configurations when certain PDUs are slower than
others.
The config defaults are the same defaults that cmdgen.UdpTransportTarget
uses (1.0 second timeout and 5 retries). The config is now reflecting
these defaults.
Closes-Bug: #1640932
Change-Id: I2490902ad2e39e8e4dc34484799a0dae96bc57f8