Make yq installation invisible for user

[l-w-2017]

No description provided.

[coveralls]

Coverage remained the same at 61.892% when pulling 32cf5c1 on install_yq into 753d1da on master.

[ChuntaoLu]

I thought you were going to vendor yq and use it the same way as thriftrw, what has changed?

[jacobgreenleaf]

I thought you were going to vendor yq and use it the same way as thriftrw, what has changed?

yq is a Python library, the only way to vendor is would be to do something like virtualenv. In general we should revisit this at a later time. The way we have usually solved this is by storing the binaries on some storage like GCS/S3 and downloading them to developer's laptop as needed.