common/rc: Add _test_dev_max_active_zones() helper function

common/rc: Add _test_dev_max_active_zones() helper function

Linux kernel 5.9 introduced a new sysfs attribute "max_active_zones". It
is an attribute of zoned block devices which indicates the limit of zones
in open or close status. To refer the attribute from test cases,
introduce the helper function _test_dev_max_active_zones(). If the
attribute is available, the function returns the attribute value.
Otherwise, returns 0 to indicate that the device does not have the limit.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>