One of the main problems a lot of developers seem to have is the issue to setting up their machines for building various platforms. This came out from the Stack overflow survey, and the number of questions on stack overflow, twitter. Etc.
It would be helpful to have a check_reqs command exposed at the CLI level. This is similar to `brew doctor` or `appium doctor`. The idea is
1. Have a way for the user to see if they have all dependencies (like JAVA_HOME or ANDROID_HOME) set up? This happens at build time, but moving it out to a CLI level command where you can run cordova check_reqs (or something similar) would be useful to the users.
2. Today, the build command shows one error at a time. The check_reqs could run all the checks, and show a summary of the issues so that the user can fix them all, instead of fixing one, running build, fixing again, etc.