Cherry-pick of "Merge branch 'ROOTUpdate-1.0-20171207' into '1.0'" into master

Update the analysis releases to LCG_91, 1.0 branch (2017.12.07.)

See merge request !198 (merged)

(cherry picked from commit ec544070)

• fbb84c29 Updated the ROOT build to use v6-10-08, in sync with LCG_91.
• 3db40113 Updated the Boost build to use 1.64.0, in sync with LCG_91.
• ff0e98b5 Updated AthAnalysisExternals to build against LCG_91 by default.