improve "No tests found..." message
improve "No tests found..." message

Summary:Relates to #856

ps. I've already signed the CLA.
Closes https://github.com/facebook/jest/pull/863

Differential Revision: D3137918

fb-gh-sync-id: e58e04b4cc8c5218cc92c9ce8cf0af97b32172f7
fbshipit-source-id: e58e04b4cc8c5218cc92c9ce8cf0af97b32172f7

mpontus/jest,Daniel15/jest,alvinsj/jest,facebook/jest,blainekasten/jest,bookman25/jest,facebook/jest,blainekasten/jest,skovhus/jest,ide/jest,alvinsj/jest,Daniel15/jest,cpojer/jest,ide/jest,aaron-goshine/jest,bookman25/jest,razh/jest,cpojer/jest,Daniel15/jest,aaron-goshine/jest,facebook/jest,sampepose/jest,ide/jest,skovhus/jest,skawian/jest,bookman25/jest,cpojer/jest,skovhus/jest,mpontus/jest,mpontus/jest,blainekasten/jest,sampepose/jest,razh/jest,skawian/jest,aaron-goshine/jest