BUGFIX: build correct node uri for multisite setup for localhost

[anselmpaul]

When using a multi-site setup and linking from one site to another, the uri generation in development does not work correctly.

Scenario:
I have a neos site "main" with domain localhost, and "other" at domain other.localhost and want to link a node from main on other.

Expected behaviour:
The generated link points to "localhost/some-node"

Actual behaviour:
The generated link points to "other.localhost/some-node"

Changes:
check if CONSTRAINT_HOST has been set before falling back to base uri

Upgrade instructions
There should be no breaking changes

Review instructions

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[skurfuerst]

I fully understand the change now, and am extremely confident this does NOT break anything else. LGTM, let's get this in :)

[skurfuerst]

the updated approach looks good to me, but I'd love to have a second review - maybe by @kitsunet ?

[kitsunet]

Thank you, this looks sensible to me.