add labels do dockerfiles, consolidate some layers

[edaniszewski]

This adds labels to the Synse Server dockerfiles to provide some image/container metadata, such as the image build date, git commit, git repo, synse version, etc. This should be helpful if there are issues when someone is using "latest" and we need to know the exact build version, e.g.

This also does a little bit of cleanup and layer consolidation as per the dockerfile "best practices"

[codecov-io]

Codecov Report

Merging #145 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #145   +/-   ##
=======================================
  Coverage   88.77%   88.77%           
=======================================
  Files          40       40           
  Lines        1114     1114           
=======================================
  Hits          989      989           
  Misses        125      125

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