v0.6.0: shipper: don't lie about webhook's identity

The webhook was getting a client that had rolloutblocks controller as
its user agent. Even though rollout blocks were indeed what the client
was being used for, that's not guaranteed to stay true forever. So let's
make sure we give the webhook a client tied to its own identity.

v0.6.0-beta.0: release controller: move cluster choosing to scheduling

This may or may not make conceptual sense (it does to me, but I could
not find out why choosing clusters and scheduling a release was two
separate steps in the first place, although after #166[1] I'm fairly
convinced this was just a technical artifact), but it sure is
convenient: we move all the error handling during the scheduling step
to a single chunk of code. This fixes an issue where errors in
ChooseClusters were not reflected in any condition, making the Release
object not change during the sync, and therefore not triggering any
events, being essentially invisible to users.

As a bonus, I restored the actual testing part of this in the unit
tests. We were previously just checking that ChooseClusters didn't
trigger any updates, without actually checking if it was doing the right
thing (choosing clusters).

[1] https://github.com/bookingcom/shipper/pull/166/files#diff-caffe52421149f1f8d77a0e7c749867dR327-R341

v0.6.0-alpha.4: capacity controller: don't retry TargetDeploymentCountError

Whenever the capacity controller can't find the exact number of
deployments it expects, it should not keep on retrying: it's impossible
for the error to resolve if deployments aren't created or deleted to
satisfy the expectation. Since the controller also listens to
deployments being created and deleted, just waiting for those events
should be enough for a new sync of the CapacityTarget to trigger, and
the controller will check again if the expectation is satisfied.

This should reduce a lot of spurious retries when a deployment just got
created and the change hasn't propagated to the informers yet, and will
also make the resync loop much faster in case shipper has a lot of
broken releases currently active.

v0.6.0-alpha.3: kubernetes: improve shipper's deployments

This brings the Shipper you deploy out of the box closer to the way we
deploy it in Booking.

This also fixes a tiny bug where the metrics port was not exposed in the
`shipper` deployment.

v0.6.0-alpha.2: installation controller: also migrate CanOverride

This was an oversight on my part in #114: by default, CanOverride will
always be false, but that's not always what's supposed to happen: if
we're migrating an InstallationTarget that belongs to a contender
release, CanOverride needs to be set to true.

This reintroduces some code that was removed in #114, but it can be
safely removed in the next version of shipper, as all objects would've
been migrated.

v0.6.0-alpha.1: shipper-state-metrics: initialize rolloutblocks lister

This fixes a panic when running the collector:

```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x116ce51]

goroutine 342 [running]:
main.ShipperStateMetrics.collectRolloutBlocks(0x1610760, 0xc00041e010, 0x1610860, 0xc00041e030, 0x1610820, 0xc00041e050, 0x16107a0, 0xc00041e070, 0x16108e0, 0xc00041e090, ...)
	/shipper/cmd/shipper-state-metrics/collector.go:351 +0x101
main.ShipperStateMetrics.Collect(0x1610760, 0xc00041e010, 0x1610860, 0xc00041e030, 0x1610820, 0xc00041e050, 0x16107a0, 0xc00041e070, 0x16108e0, 0xc00041e090, ...)
	/shipper/cmd/shipper-state-metrics/collector.go:101 +0x194
github.com/prometheus/client_golang/prometheus.(*Registry).Gather.func1()
	/shipper/vendor/github.com/prometheus/client_golang/prometheus/registry.go:434 +0x19d
created by github.com/prometheus/client_golang/prometheus.(*Registry).Gather
	/shipper/vendor/github.com/prometheus/client_golang/prometheus/registry.go:445 +0x571
```

v0.6.0-alpha.0: Update chart.go (#186)

fix  #145

v0.5.0-beta.0: Chart repo errors are wrapped in Shipper errors fixes #152

This change is aiming to turn helm library errors into Shipper errors so
the responsible caller gets an idea if the error should be retried.

Signed-off-by: Oleg Sidorov <oleg.sidorov@booking.com>

v0.5.0-alpha.6: Chart repo errors are wrapped in Shipper errors fixes #152

This change is aiming to turn helm library errors into Shipper errors so
the responsible caller gets an idea if the error should be retried.

Signed-off-by: Oleg Sidorov <oleg.sidorov@booking.com>

v0.5.0: Chart repo errors are wrapped in Shipper errors fixes #152

This change is aiming to turn helm library errors into Shipper errors so
the responsible caller gets an idea if the error should be retried.

Signed-off-by: Oleg Sidorov <oleg.sidorov@booking.com>