[maint] Do not modify the options hash in apply_manifest_on

1) This is just poor behavior
2) When an array of hosts is passed, apply_manifest_on is run more
than once. In this situation, the first one modifies the options hash
and ruins it for all its friends
Merge pull request #147 from branan/we_wouldnt_have_this_problem_in_clojure

[maint] Do not modify the options hash in apply_manifest_on