Support for unassigning IPs (#422)

* Support for unassigning IPs

* When WARM_IP_TARGET is set, unassign IPs if the number of
available IPs is greater than the WARM_IP_TARGET.
* Unassigns from all ENIs at once.

* Unassign ips after deleting them from the store

* This removes the possibility that unassigned
  ips are used by other pods before they can
  be deleted from the store.  If they are removed
  and deletion fails, the reconciler will add them
  back to the store.

* GO111MODULE for travis

.travis.yml

@@ -23,7 +23,7 @@ install:
 
 # Tests to run
 script:
-  - make build-linux
-  - make lint
-  - make vet
-  - make unit-test
+  - GO111MODULE=on make build-linux
+  - GO111MODULE=on make lint
+  - GO111MODULE=on make vet
+  - GO111MODULE=on make unit-test

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/containernetworking/cni v0.5.2
 	github.com/coreos/go-iptables v0.4.0
 	github.com/davecgh/go-spew v1.1.1
+	github.com/deckarep/golang-set v1.7.1
 	github.com/docker/distribution v2.6.2+incompatible
 	github.com/docker/docker v1.13.1
 	github.com/docker/go-connections v0.4.0

go.sum

@@ -11,6 +11,8 @@ github.com/coreos/go-iptables v0.4.0 h1:wh4UbVs8DhLUbpyq97GLJDKrQMjEDD63T1xE4Crs
 github.com/coreos/go-iptables v0.4.0/go.mod h1:/mVI274lEDI2ns62jHCDnCyBF9Iwsmekav8Dbxlm1MU=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/deckarep/golang-set v1.7.1 h1:SCQV0S6gTtp6itiFrTqI+pfmJ4LN85S1YzhDf9rTHJQ=
+github.com/deckarep/golang-set v1.7.1/go.mod h1:93vsz/8Wt4joVM7c2AVqh+YRMiUSc14yDtF28KmMOgQ=
 github.com/docker/distribution v2.6.2+incompatible h1:4FI6af79dfCS/CYb+RRtkSHw3q1L/bnDjG1PcPZtQhM=
 github.com/docker/distribution v2.6.2+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
 github.com/docker/docker v1.13.1 h1:IkZjBSIc8hBjLpqeAbeE5mca5mNgeatLHBy3GO78BWo=