Cleanup after Powershell install for CentOS/Fedora Docker Images#6264

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TravisEz13 merged 2 commits intoPowerShell:masterfrom

strawgate:master

Mar 1, 2018

Commits on Feb 28, 2018

Adding "yum clean all" to CentOS 7 Dockerfile reduces docker image size by 76MB
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Adding "dnf clean all" to Fedora Dockerfile reduces docker image size by 168MB
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committed