jsonrpc: reuse existing connection
jsonrpc: reuse existing connection

Keep a connection reference at module level to be
reused by future requests if still valid.

Change-Id: I82e8b842096f54ae74d62bcd48c079fa7b4a1b1d
Requires: https://gerrit.ovirt.org/58029
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1417708
Signed-off-by: Simone Tiraboschi <cb03129c66ba4da7ba7044049d0f43907bf857bb@redhat.com>

oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha