Change from glide to dep

[zhexuany]

Not sure which version should I add to Gopkg.toml. Please comment in this PR, so I can change it later. Now dep supports prune operation which allow use prune test files and non-go files. In future, this could be absorbed into ensure operation. But this is still in progress. As for now, we have to run dep prune after dep ensure.

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This change is 

[zhexuany]

Before:
If we run find _vendor/ -type f | wc -l, only 799 files are vended.
After:
If we run find vendor -type f | wc -l, 1555 files are vended.

Not sure is it worth to change to dep.

[zhexuany]

just come up with a script call clean_vendor.sh in directory hack. We can execute it and delete all irrelevant files. By do this, only 800 files in vendor.

[coocood]

@zhexuany
What's the difference between manual delete tests file and [prune] in gopkg.toml?

[zhexuany]

dep prune only deletes some *_test.go but not all of them.
Here is the guide for reproducing:

1. run dep ensure
2. find vendor/ -name "*_test.go" | wc -l gives us 851.
3. run dep prune
4. find vendor/ -name "*_test.go" | wc -l gives us 374.

The number means how many *_test.go is still in vendor.

[coocood]

@zhexuany
Can you find the reason why those test files are not deleted?

[zhexuany]

@coocood

Check this issue golang/dep#944
It is on progress. dep prune should have full functionality after closing this issue. dep team is currently working on this.

[coocood]

@zhexuany
The assembly files should not be deleted.
So I think manually delete files is not safe.

[zhexuany]

@coocood
agreed.
Maybe can change it to just delete certain files like *_test.go and .gitignore and etc.