Disk and Network method performance and thread safety

[dbwiddis]

Fixes #1106

[coveralls]

Coverage remained the same at 78.838% when pulling f4fb5c5 on dbwiddis:threadsafe into 0cee9ab on oshi:master.

[codecov-io]

Codecov Report

Merging #1107 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1107      +/-   ##
============================================
- Coverage     74.72%   74.66%   -0.06%     
  Complexity        2        2              
============================================
  Files            27       27              
  Lines          1341     1342       +1     
  Branches        169      170       +1     
============================================
  Hits           1002     1002              
- Misses          262      263       +1     
  Partials         77       77

Impacted Files	Coverage Δ	Complexity Δ
...i-demo/src/main/java/oshi/demo/OshiHTTPServer.java	0% <0%> (ø)	0% <0%> (ø)	⬇️

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