Fail image_optim hook if gem not installed
Fail image_optim hook if gem not installed

Change-Id: Icf2375dd0bfff642dda075f6b8e298b4aed2ca93
Reviewed-on: http://gerrit.causes.com/47046
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@brigade.com>
Reviewed-by: Shane da Silva <67fb7bfe39f841b16a1f86d3928acc568d12c716@brigade.com>

gnagel/overcommit,blech75/overcommit,TheSooth/overcommit,TheSooth/overcommit,oxocode/overcommit,blech75/overcommit,oxocode/overcommit,gnagel/overcommit