http: add type checking for hostname

[jasnell]

Add type checking for options.hostname / options.host Maintains the use of undefined and null for default localhost, but other falsy values (like false, 0 and NaN) are rejected.

Refs: #12488

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

http