only try to install plugins if install_method is not none
only try to install plugins if install_method is not none

codilime/cloudify-plugins-common,cloudify-cosmo/cloudify-plugins-common,cloudify-cosmo/cloudify-plugins-common,isaac-s/cloudify-plugins-common,codilime/cloudify-plugins-common,isaac-s/cloudify-plugins-common,cloudify-cosmo/cloudify-plugins-common,codilime/cloudify-plugins-common,isaac-s/cloudify-plugins-common