cf: make ipsec optional
cf: make ipsec optional

https://www.pivotaltracker.com/n/projects/1275640/stories/174773005

we are removing ipsec because the release is deprecated and we do not
need it anymore because we have mtls between gorouter and apps (which
satisfies the e2e encryption requirement)

Signed-off-by: Toby Lorne <527052641d65eef236eeef9545b2acac74c35d57@digital.cabinet-office.gov.uk>

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf