cpanminus install should benefits of perl::module $exec_environment

Sometimes, outgoing HTTP connections must use a proxy, so cpanminus installation must also make use of $exec_environment passed to puppet::module otherwise the install process will fail.

cpanminus installation should also honor $exec_timeout parameter (in this case default values don't change anything).

Merging the two files also prevent useless require on cpanminus if somebody only want to install perl modules from packages.