Bug 1053471 Parse a string to multiple env vars of an array of hashes

https://bugzilla.redhat.com/show_bug.cgi?id=1053471

When setting multiple env vars with SET_UNSET_ENVIRONMENT_VARIABLES API, and in the runtime of
adding cartridges(ADD_CARTRIDGE) or creating apps(ADD_APPLICATION), user_env_vars is passed as
a raw string, and thus, the variable cannot be recoganized as an array of hashes. The fixes
include:

1. parse user_env_vars and return the parsed data (Application.validate_user_env_variables)
2. modify the methods invoking Application.validate_user_env_variables (
   EnvironmentVariablesController, ApplicationsController, EmbCartController)