Construct urls using url.format()

[tprobinson]

This fixes strange errors when the requested path does not begin with a slash.

Also fix a test that wouldn't work by using os.hostname() to create a localhost-like name.

[coveralls]

Pull Request Test Coverage Report for Build 406

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 97.309%

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Totals
Change from base Build 404:	0.01%
Covered Lines:	138
Relevant Lines:	142

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💛 - Coveralls

[tprobinson]

Closed in favor of #580