This adds constraints for asserting that a given attribute or value
exists, or does not exist. This acts as a companion to =, or !=
operators, e.g:
```hcl
constraint {
attribute = "${attrs.type}"
operator = "!="
value = "database"
}
constraint {
attribute = "${attrs.type}"
operator = "is_set"
}
```
In state values, we need to be able to distinguish between zero values
(e.g. `false`) and unset values (e.g. `nil`).
We can alternatively use protobuf `oneOf` and nested map to ensure
consistency of fields that are set together, but the golang
representation does not represent that well and introducing a mismatch
between representations. Thus, I opted not to use it.
* upgrade Nomad from 0.8.4 to 0.8.6
* update deprecated nomad and vault commands
* update AMI ID
* add ingress rule for default fabio port and fabio UI
* upgrade Consul and Vault versions
* update AMI ID in README.md and terraform.tfvars
This commit allows the ConstraintChecker to test values that do not exist.
This is useful when wanting to _exclude_ given nodes from executing a
job, for example, if you wanted to give canary nodes an attribute, and
not run critical services on them, you may specify something like the
below, but not want to tag all other nodes with the inverse.
```hcl
constraint {
attribute = "${node.attr.canary}
operator = "!="
value = "1"
}
```
This also requires all constraint checkers to allow for nil target
values, as they will no longer be short circuited by resolving a target.
We run with ~120 apt sources, and apt-get update fails if any of them is
down.
True errors would be raised again at install phase as true dependencies
fetch would fail.
;
nomad/client take very long and exceed 15m sometimes:
In https://travis-ci.org/hashicorp/nomad/jobs/452990197 :
```
panic: test timed out after 15m0s
goroutine 4739 [running]:
testing.(*M).startAlarm.func1()
/home/travis/.gimme/versions/go1.11.2.linux.amd64/src/testing/testing.go:1296 +0xfd
....
goroutine 4665 [select]:
github.com/hashicorp/nomad/vendor/google.golang.org/grpc.newClientStream.func5(0xc0003dd500, 0xc000420120, 0x2b3f86295588, 0xc000496810)
/home/travis/gopath/src/github.com/hashicorp/nomad/vendor/google.golang.org/grpc/stream.go:287 +0xd7
created by github.com/hashicorp/nomad/vendor/google.golang.org/grpc.newClientStream
/home/travis/gopath/src/github.com/hashicorp/nomad/vendor/google.golang.org/grpc/stream.go:286 +0x842
FAIL github.com/hashicorp/nomad/client/driver 900.036s
```
