Fix bug related to config overwrite

[vrde]

Calling bigchaindb configure would overwrite the original config even if the user answered n.

This PR is to fix this wrong behavior.

[r-marques]

👍

[codecov-io]

Current coverage is 83.29%

Merging #97 into develop will increase coverage by +83.29% as of ca54948

@@            develop     #97   diff @@
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  Files             0      15    +15
  Stmts             0     778   +778
  Branches          0       0       
  Methods           0       0       
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+ Hit               0     648   +648
  Partial           0       0       
- Missed            0     130   +130

Review entire Coverage Diff as of ca54948

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