testing: make the output of -v more uniform and aligned when using fixed-width fonts

Delete the colon from RUN: for examples, since it's not there for tests.
Add spaces to line up RUN and PASS: lines.

Before:
=== RUN TestCount
--- PASS: TestCount (0.00s)
=== RUN: ExampleFields
--- PASS: ExampleFields (0.00s)

After:
=== RUN   TestCount
--- PASS: TestCount (0.00s)
=== RUN   ExampleFields
--- PASS: ExampleFields (0.00s)

Fixes #10594.

Change-Id: I189c80a5d99101ee72d8c9c3a4639c07e640cbd8
Reviewed-on: https://go-review.googlesource.com/9846
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/testing/testing.go

@@ -557,7 +557,7 @@ func RunTests(matchString func(pat, str string) (bool, error), tests []InternalT
 			}
 			t.self = t
 			if *chatty {
-				fmt.Printf("=== RUN %s\n", t.name)
+				fmt.Printf("=== RUN   %s\n", t.name)
 			}
 			go tRunner(t, &tests[i])
 			out := (<-t.signal).(*T)