Fixes #15277 - use yum erase instead of rpm -e. (#354)

The gutterball removal requests the removal of a handful of packages.
If any are missing with `rpm -e`, the entire command will fail.
However, if you use `yum erase`, the missing packages will not cause an
issue and the remaining packages will be removed. Additionally, `yum
erase` will return a zero exit code in this case.

Logic was also added to cover both the `tomcat` and `tomcat6` dirs
during cleanup.

hooks/post/30-upgrade.rb

@@ -42,8 +42,12 @@ def remove_docker_v1_content
 
 def remove_gutterball
   return true unless Kafo::Helpers.execute('rpm -q gutterball')
-  Kafo::Helpers.execute("rpm -e gutterball tfm-rubygem-foreman_gutterball gutterball-certs tfm-rubygem-hammer_cli_gutterball")
-  Kafo::Helpers.execute("rmdir /var/lib/tomcat/webapps/gutterball")
+  Kafo::Helpers.execute("yum erase -y gutterball tfm-rubygem-foreman_gutterball gutterball-certs tfm-rubygem-hammer_cli_gutterball")
+
+  ['tomcat', 'tomcat6'].each do |t|
+    gutterball_dir = "/var/lib/#{t}/webapps/gutterball"
+    Kafo::Helpers.execute("rmdir #{gutterball_dir}") if File.directory?(gutterball_dir)
+  end
 end
 
 def upgrade_step(step, options = {})