CLOUDIFY-2251
CLOUDIFY-2251

1. Separate plugin installer verification method and get arguments into two methods.
2. verify method has a throw_on_failure indicator whether it should raise an exception or return False when verification is failed

codilime/cloudify-manager,isaac-s/cloudify-manager,geokala/cloudify-manager,konradxyz/cloudify-manager,konradxyz/dev_fileserver,codilime/cloudify-manager,geokala/cloudify-manager,codilime/cloudify-manager,isaac-s/cloudify-manager,isaac-s/cloudify-manager,cloudify-cosmo/cloudify-manager,cloudify-cosmo/cloudify-manager,konradxyz/dev_fileserver,konradxyz/cloudify-manager,cloudify-cosmo/cloudify-manager