ref(tests): move test commands into code

Deis' integration tests are more approachable without the
indirection of looking them up from a JSON fixture.
ref(tests): move exported Test* funcs to top of files and tidy up code
ref(tests): combine and shorten names of Go utility packages
fix(tests): remove GetCommand() func and vendored simplejson package
Merge pull request #1527 from deis/test-integration-no-json

ref(tests): clean up and pare down test code