conf/domain_conf: use virStringParseYesNo helper

conf/domain_conf: use virStringParseYesNo helper

This helper performs a conversion from a "yes|no" string
to a corresponding boolean, and several conversions were
already done, but there are still some omissions.

For most of the remaining usages in domain_conf.c only
"yes" is explicitly checked for. This means all other
values are implicitly handled as 'false'. In this case,
use virStringParseYesNo to handle the conversion and
reserve the original logic of not raise an error, so
ignore the return value of helper.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>