MB-9612: do some exponential backoff retries on tmperrors in xmem
MB-9612: do some exponential backoff retries on tmperrors in xmem

Change-Id: I92dae9b1678524fe1fed7598f3b46ce5c0732a6d
Reviewed-on: http://review.couchbase.org/39373
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

nimishzynga/ns_server,membase/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,membase/ns_server,ceejatec/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,mschoch/ns_server,mschoch/ns_server,mschoch/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,membase/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,ceejatec/ns_server