Make Travis go faster
Make Travis go faster

Since we're compiling things like protobuf from scratch, it makes a lot
of sense to cache the blaze-bin directories. This really plays to
Bazel's strengths, which is that it solves the cache invalidation
problem.

Results: Rather than taking 8 minutes, Travis now takes somewhere
between two minutes and eight minutes.

shakedel/tensorboard,shakedel/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,ioeric/tensorboard,shakedel/tensorboard,agrubb/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,tensorflow/tensorboard,agrubb/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,ioeric/tensorboard,ioeric/tensorboard,ioeric/tensorboard,tensorflow/tensorboard,agrubb/tensorboard,agrubb/tensorboard,francoisluus/tensorboard-supervise,qiuminxu/tensorboard,tensorflow/tensorboard,agrubb/tensorboard,shakedel/tensorboard,ioeric/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,agrubb/tensorboard,tensorflow/tensorboard,qiuminxu/tensorboard,ioeric/tensorboard,shakedel/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,shakedel/tensorboard