What does this PR (Pull Request) do?

This PR includes various improvements to the CDN in a Box Makefile:

• Allows you to use the Makefile even if a parent directory name contains a space

• Allows you to run the Makefile without needing to be in the CDN in a Box directory

• This PR is not related to any Issue

Which Traffic Control components are affected by this PR?

• CDN in a Box

What is the best way to verify this PR?

• In ${GOPATH}/src/github.com/apache, rename the trafficcontrol directory to Traffic Control with a space.
• In the Traffic Control directory, use the CDN in a Box Makefile to build the RPMs:

  make -f infrastructure/cdn-in-a-box/Makefile

• Test the RPMs in CDN in a Box

If this is a bug fix, what versions of Traffic Control are affected?

• master (8f6365f)
• 5.1.0

The following criteria are ALL met by this PR

• Building CDN in a Box is a sufficient test, additional tests are unnecessary
• The CDN in a Box documentation page does not mention not being able to use spaces, documentation is unnecessary
• An update to CHANGELOG.md is not necessary
• This PR includes any and all required license headers
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)