(MODULES-10950) Infer application name from run mode

Fix a regression introduced by MODULES-7397[1] which incorrectly assumed
that the application name can be queried through
`Puppet::Application.name`, causing lenses that are pluginsynced not to
be loaded.

Since we only need to find out whether or not we're running as part of
`puppet agent`, it should be enough to use `Puppet.run_mode.name`, which
returns `:agent` in this case, and `:user` otherwise.

[1] #27

Author: GabrielNagy

lib/puppet/provider/augeas/augeas.rb

@@ -367,7 +367,7 @@ def get_load_path(resource)
       load_path.flatten!
     end
 
-    if Puppet::Application.name == :agent
+    if Puppet.run_mode.name == :agent
       if Puppet::FileSystem.exist?("#{Puppet[:libdir]}/augeas/lenses")
         load_path << "#{Puppet[:libdir]}/augeas/lenses"
       end

spec/unit/provider/augeas/augeas_spec.rb

@@ -1124,7 +1124,7 @@ def make_tmpname((prefix, suffix), n)
     context 'when running application is agent' do
       before(:each) do
         Puppet[:libdir] = my_fixture_dir
-        Puppet::Application.stubs(:name).returns(:agent)
+        Puppet.run_mode.stubs(:name).returns(:agent)
       end
 
       it 'offers pluginsync augeas/lenses subdir' do
@@ -1139,7 +1139,7 @@ def make_tmpname((prefix, suffix), n)
 
     context 'when running application is not agent' do
       before(:each) do
-        Puppet::Application.stubs(:name).returns(:apply)
+        Puppet.run_mode.stubs(:name).returns(:user)
 
         env = Puppet::Node::Environment.create('root', ['/modules/foobar'])
         Puppet.stubs(:lookup).returns(env)