test: use dot-relative imports where appropriate

test: use dot-relative imports where appropriate

Currently, run.go's *dir tests allow "x.go" to be imported
interchangeably as either "x" or "./x". This is generally fine, but
can cause problems when "x" is the name of a standard library
package (e.g., "fixedbugs/bug345.dir/io.go").

This CL is an automated rewrite to change all `import "x"` directives
to use `import "./x"` instead. It has no effect today, but will allow
subsequent CLs to update test/run.go to resolve "./x" to "test/x" to
avoid stdlib collisions.

Change-Id: Ic76cd7140e83b47e764f8a499e59936be2b3c876
Reviewed-on: https://go-review.googlesource.com/c/go/+/395116
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>