vlsingle, vmsingle, vtsingle: do not mount emptyDir if data volume is present in spec.volumes

[AndrewChubatiuk]

currently it's only possible to set external PVC for vlsingle and vmsingle only with crutches: storageDataPath should be set using spec.extraArgs, since default or one, which is controlled by spec.storageDataPath creates PVC from spec.storage or mounts emptyDir if spec.storage is not set. any volume mounts that are mounted to spec.storageDataPath lead to collision. Even with this crutch pod has unneeded volume mount, also in vmsingle backup functionality becomes unavailable, since it also relies on spec.storageDataPath value.

this PR moves method, which mounts storage volume to build package and does the following:

• adds volume mount that points to storageDataPath only if volume with expected name data is not already present in spec.volumeMounts
• adds volume with managed PVC if spec.storage is defined
• adds emptyDir volume only storage volume is not found in spec.volumes
• fails if any volume with other name, than data mount path intersects with storageDataPath
• fails if volume with name data doesn't intersect with storageDataPath

fixes #784

[vrutkovs]

We should be checking that StorageDataPath is listed in one of the volumes

[AndrewChubatiuk]

updated PR

[vrutkovs]

I was thinking about extending tests too:

Expect(ts.Volumes[0].EmptyDir).ToNot(BeNil())
Expect(ts.Containers[0].VolumeMounts[0].MountPath).To(Equal("/tmp/"))

and so on in other testcases too

[f41gh7]

Lets be careful with this change. It potentially may break exist deployments of VMSingle instances, I'd like to keep it backward-compatible.

[AndrewChubatiuk]

@f41gh7 @vrutkovs
updated implementation and description

[lexfrei]

Related to #1677