[OTFC] Make separate config inits for client & daemon use.

Summary:
The config can be initialized with config.New() of config.NewWritable()
New() mmaps with READ only protection mode. NewWritable() mmaps with READ|WRITE protection mode.

Test Plan:
  $ bin/gocov test github.com/gow/otfc/ | tee /tmp/qqq/1 | bin/gocov report | sort
  ok    github.com/gow/otfc 0.090s

  github.com/gow/otfc/     --------  53.85% (7/13)
  github.com/gow/otfc//otfc.go   Delete    100.00% (1/1)
  github.com/gow/otfc//otfc.go   Get     100.00% (1/1)
  github.com/gow/otfc//otfc.go   Init    100.00% (2/2)
  github.com/gow/otfc//otfc.go   Print     0.00% (0/4)
  github.com/gow/otfc//otfc.go   Set     100.00% (1/1)
  github.com/gow/otfc//otfc.go   Shutdown  50.00% (2/4)

Reviewers: tommy.testy

Reviewed By: tommy.testy

Maniphest Tasks: T6

Differential Revision: http://dev.chetan.io/D35