IMPALA-5557: Disable rpc_default_keepalive_time_ms
IMPALA-5557: Disable rpc_default_keepalive_time_ms

This change makes sure backend connections with KRPC are always
kept alive by disabling the idle connection detection logic.

Idle connections all tend to be closed and re-opened around the
same time, which may easily lead to negotiation timeouts. Until
KUDU-279 is fixed, closing idle connections is also racy and leads
to query failures.

This disablement was validated with Kudu's rpc-test.

Change-Id: I0871dd9c9bbe455466b9b2d2a2bbedec79cf0775
Reviewed-on: http://gerrit.cloudera.org:8080/8910
Reviewed-by: Michael Ho <43544f6c6f19372b140301f92a3768afc300868a@cloudera.com>
Reviewed-by: Sailesh Mukil <a0dfbcae8e92bb4f48772d8c6743e175570f6f74@cloudera.com>
Tested-by: Impala Public Jenkins

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala