[dev] Replace istanbul with nyc

从 grunt test 命令开始，找到 CLI 使用的 Istanbul 依赖项和 coverage 配置。检查 Jenkins 构建如何接收测试失败，并根据当前会触发语法错误的 destructuring 示例验证迁移。完成的标准是测试使用 nyc 运行，并且 coverage 错误产生非零状态。

As the istanbul package is not longer maintained, we need to migrate to nyc.
Currently istanbul doesn't work for the following code:

const { stdio = "inherit" } = options;

In this case grunt test command fails with an exception:

__cov_gCRxMpJElFAq6oDSOHYQNQ.s['1']++;var __awaiter=(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][0]++,this)&&(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][1]++,this.__awaiter)||(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['1'][2]++,function(thisArg,_arguments,P,generator){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['1']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['2']++;return new((__cov_gCRxMpJElFAq6oDSOHYQNQ.b['2'][0]++,P)||(__cov_gCRxMpJElFAq6oDSOHYQNQ.b['2'][1]++,P=Promise))(function(resolve,reject){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['2']++;function fulfilled(value){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['3']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['4']++;try{__cov_gCRxMpJElFAq6oDSOHYQNQ.s['5']++;step(generator.next(value));}catch(e){__cov_gCRxMpJElFAq6oDSOHYQNQ.s['6']++;reject(e);}}function rejected(value){__cov_gCRxMpJElFAq6oDSOHYQNQ.f['4']++;__cov_gCRxMpJElFAq6oDSOHYQNQ.s['8']++;try{__cov_gCRxMpJElFAq6oDSOHYQNQ.s['9']++;step(generator['throw'](value));}catch(e){__cov_gCRxMpJElFAq6oDSO

SyntaxError: Unexpected token :
    at new Script (vm.js:79:7)
    at createScript (vm.js:251:10)
    at Object.runInThisContext (vm.js:303:10)
    at Module._compile (internal/modules/cjs/loader.js:656:28)
    at Object.Module._extensions.(anonymous function) [as .js] (/Users/havaluova/Work3/nativescript-cli/node_modules/istanbul/lib/hook.js:107:24)
    at Module.load (internal/modules/cjs/loader.js:598:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:537:12)
    at Function.Module._load (internal/modules/cjs/loader.js:529:3)
    at Module.require (internal/modules/cjs/loader.js:636:17)
    at require (internal/modules/cjs/helpers.js:20:18)

It seems that when the above mentioned error occurs, istanbul exits with status code 0 and this is the reason why jenkins build doesn't fail in such situation.