python/rpc: Change num arg to default for bdev_error_injection_error

If we add default arguments to the bdev_error_injection_error RPC,
it causes a syntax error, non-default argument follows default
argument.

The RPC handler initializes the value of the num argument to be 1
if it is omitted. Hence, the RPC client can make the num argument
from non-default to default by removing =1. Otherwise, we have to
insert new default argument before the num argument.

Signed-off-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Change-Id: I0eb009ff3c0c5078f2afc4fa15e9ac97feeb0846
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/15023


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Pawel Piatek <pawelx.piatek@intel.com>