Customize the command used to install CocoaPods

From @NathanWalker on March 19, 2016 23:55

Because some CocoaPods can be finicky at best to get working with {N} plugins, it would probably help to be able to customize or specify a command to run a pod install.
For example, please see this issue:
https://github.com/segment-integrations/analytics-ios-integration-google-analytics/issues/3#issuecomment-164874798

The issue arises from the Segment-GoogleAnalytics pod and the solution posted above involves a custom install of CocoaPods and the usage of bundle exec pod install along with a Gemfile to circumvent the issues.

It would be nice that when running tns emulate ios with CocoaPods involved, a command line argument could be passed to provide a custom pod install command to be able to use this solution.

Working on this {N} plugin for Segment:
https://github.com/NathanWalker/nativescript-segment
Blocked by this at moment.

Copied from original issue: NativeScript/ios-runtime#535

从 tns emulate ios 流程开始，跟踪 CocoaPods 在哪里运行 pod install。检查所请求的 bundle exec pod install 和 Gemfile workaround，然后定义如何提供自定义命令。完成标准是 iOS 模拟流程可以为需要自定义 CocoaPods 安装的项目使用该命令。