Improve Travis CI build Performance

[chenzhang22]

trafficstars

Caching Dependencies and Directories Travis CI can cache content that does not often change, to speed up the build process.

===================== If there are any inappropriate modifications in this PR, please give me a reply and I will change them.

[afsanjar]

Could we try to enable power? please add below to .travis.yml file.

arch: 
  ppc64le

[chenzhang22]

ok