Refactor --subdomains flag in the Install WP task
Refactor --subdomains flag in the Install WP task

According to the
[documentation](https://developer.wordpress.org/cli/commands/core/multisite-install/)
the existance of the --subdomains is boolean value. If the
item.value.multisite.subdomains was set to false (or not set) this task
was treating it as it's set to true.

This commit is fixing this.

pressbooks/trellis,roots/trellis,kalenjohnson/trellis,jeffstieler/bedrock-ansible,buluma/trellis,kalenjohnson/trellis,roots/bedrock-ansible,partounian/trellis,newtonne/trellis,NicBeltramelli/trellis,NicBeltramelli/trellis,newtonne/trellis,partounian/trellis,proteusthemes/pt-ops,kalenjohnson/trellis,kalenjohnson/trellis,buluma/trellis,NicBeltramelli/trellis,jeffstieler/bedrock-ansible,proteusthemes/pt-ops,NicBeltramelli/trellis,cimocimocimo/cimo-wordpress-server,jeffstieler/bedrock-ansible,buluma/trellis,partounian/trellis,cimocimocimo/cimo-wordpress-server,roots/trellis,newtonne/trellis,pressbooks/trellis,cimocimocimo/cimo-wordpress-server,buluma/trellis,partounian/trellis,roots/bedrock-ansible,proteusthemes/pt-ops,cimocimocimo/cimo-wordpress-server