Remove 'ignore_errors: true' in favor of 'failed_when: false'

This change removes the use of 'ignore_errors: true' because it causes deployers
to see red output and a stacktrace, which traditionally means something is broken,
even when the failure is known to have a fall back option or be intentional. This
conversion will provide a generally cleaner interface.

It should be noted that the 'failed' filter will still function normally. Tasks
with the 'failed_when: false' option will still be marked as 'failed' in any
registered variable. This change simply makes the output look cleaner.

Change-Id: I298510082bcecb0b84eb252851f8044d8b7f7f61
Closes-Bug: #1633438
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>

tasks/lxc_cache.yml

@@ -24,7 +24,7 @@
   retries: 3
   delay: 10
   until: cache_download_primary | success
-  ignore_errors: yes
+  failed_when: false
   tags:
     - lxc-cache
     - lxc-cache-download

tasks/lxc_kernel_tuning.yml

@@ -20,5 +20,5 @@
     sysctl_set: "{{ item.set|default('yes') }}"
     state: "{{ item.state|default('present') }}"
     reload: "{{ item.reload|default('yes') }}"
-  ignore_errors: true
+  failed_when: false
   with_items: "{{ lxc_kernel_options }}"