(SERVER-2192) Use environment name string for listing tasks
(SERVER-2192) Use environment name string for listing tasks

When requesting a list of tasks, pass the requested environment as a
string rather than a symbol. The environment cache is primarily used
with string; pass as a string to ensure we re-use a cached environment
if available and avoid registering a cached environment based an a
symbol rather than string name.

puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppet-server,puppetlabs/puppet-server,puppetlabs/puppetserver