Checks if app already has ingress before trying to reserve a static IP

[retpolanne]

This PR checks if the app has a Teresa managed ingress before trying to reserve a static IP.

Fixes #634

[codecov-commenter]

Codecov Report

Merging #635 into master will decrease coverage by 0.04%. The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #635      +/-   ##
==========================================
- Coverage   50.52%   50.48%   -0.05%     
==========================================
  Files          86       86              
  Lines        6221     6224       +3     
==========================================
- Hits         3143     3142       -1     
- Misses       2865     2867       +2     
- Partials      213      215       +2     

Impacted Files	Coverage Δ
pkg/server/deploy/deploy.go	73.86% <50.00%> (-1.65%)	:arrow_down:
pkg/server/cloudprovider/gce.go	87.87% <100.00%> (ø)

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[retpolanne]

@drgarcia1986 done!