qemu/qemu_migration_params: use virStringParseYesNo helper

qemu/qemu_migration_params: use virStringParseYesNo helper

A function virStringParseYesNo was added to convert
string 'yes' to true and 'no' to false, so use this
helper to replace 'STREQ(.*, \"yes\")' and
'STREQ(.*, \"no\")' as it allows us to drop several
repetitive if-then-else string->bool conversion blocks.

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>