Use constants instead of  hardcoded `android` and  `ios` strings

**Is your feature request related to a problem? Please describe.**
We have "android", "Android", "ANDROID" and "ios", "iOS", "IOS" hardcoded in many places in the CLI. In most of the places, we are also using platform.toLower() in order to workaround this.

**Describe the solution you'd like**
We should just use the same constants everywhere (e.g. DevicePlatformsConstants)