Fixed composer installing non prod dependencies

[amansilla]

The composer flag --no-dev should be used in order to
avoid installing dependencies not necessaries on a production
environment.

[davidalger]

@amansilla Would you agree it would make sense to case the use of this flag such that it's only set if the (currently existing) :magento_deploy_production setting is true (default value)? That way if this is used to deploy to a stage or CI server where phpunit and the like is needed, they can be used if so desired.

Currently an if fetch(:magento_deploy_production) is being used to allow disabling compilation and static asset generation.

[davidalger]

@amansilla I went ahead and merged this into develop and then added a check for the aforementioned flag. This will be included in the next tagged release, which should be coming shortly.

[davidalger]

And a note on this… since Magento 2.0 breaks when --no-dev is specified (see magento/magento2#2561) I have implemented a check in commit f4a095e to first install the code, check the version number and then add --no-dev to the set of flags used for deployment. The end result is the same for 2.1 and later installs, but maintains compatibility with 2.0 installs.