go/types: add more logging to gc import test
go/types: add more logging to gc import test

* Extended deadline to 30 seconds
* Added logging of the duration of each package import
* Fail the test immediately if directories cannot be read

R=gri, minux.ma
CC=golang-dev
https://codereview.appspot.com/7030055

gnanderson/go,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,apparentlymart/golang,dsriram/golang,tv42/old-go,apparentlymart/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,gnanderson/go,dsriram/golang,dsriram/golang,tv42/old-go,apparentlymart/golang,gnanderson/go