cmd/go: clarify test filenames in help messages

Fixes #5655.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/9944044

src/cmd/go/doc.go

@@ -396,8 +396,8 @@ It prints a summary of the test results in the format:
 
 followed by detailed output for each failed package.
 
-'Go test' recompiles each package along with any files with names matching
-the file pattern "*_test.go".  These additional files can contain test functions,
+'Go test' recompiles each package along with any files with names ending in
+"_test.go".  These additional files can contain test functions,
 benchmark functions, and example functions.  See 'go help testfunc' for more.
 Each listed package causes the execution of a separate test binary.
 

src/cmd/go/test.go

@@ -45,8 +45,8 @@ It prints a summary of the test results in the format:
 
 followed by detailed output for each failed package.
 
-'Go test' recompiles each package along with any files with names matching
-the file pattern "*_test.go".  These additional files can contain test functions,
+'Go test' recompiles each package along with any files with names ending in
+"_test.go".  These additional files can contain test functions,
 benchmark functions, and example functions.  See 'go help testfunc' for more.
 Each listed package causes the execution of a separate test binary.