pkg/testutils: utility functions to facilitate writing Go tests

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Add Cristian as maintainer to pkg/testutils

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Fix format in maintainers files

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Merge pull request #6145 from shykes/pr_out_pkg_testutils_utility_functions_to_facilitate_writing_go_tests

pkg/testutils: utility functions to facilitate writing Go tests