Extract hard-coded constants to configurable variables

[aklenik]

Currently, some values are hard-coded, e.g., the timeout for chaincode instantiation (#137). A proper configuration support should be added to Caliper.

The two aspects:

1. The library: I propose nconf, the Fabric SDK uses it, and wrote an elegant wrapper class for it (reusing this wrapper class without introducing the SDK as a constant dependency is another question).
2. The conventions: I propose a naming convention like in Fabric, since Caliper also has some major submodules. For example, the current OVERWRITE_GOPATH setting could be something like
   CALIPER_FABRIC_OVERWRITEGOPATH

@haojun Opinions?

[haojun]

@panyu4 @jiangyaoguo

[aklenik]

Implemented by PR #202