Make logo lead to /#: it works better with a path_prefix

[michaelklishin]

Proposed Changes

This makes the logo lead to /#: it works better when a management.path_prefix is used.

Taking the user to / with a path_prefix actually works just
fine if the / is accessiable: that will redirect to the prefixed root.
However, if / is not served by the HTTP API (think of a reverse proxy
in front of it mediating and controlling access), that will fail.

/# should not suffer from this problem. In fact, that's what the Overview tab has been using for years.

Types of Changes

• Bug fix (non-breaking change which fixes issue Logo link does not honor the configured path prefix #604)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

Further Comments

Closes #604.

[#161479342]