Provide ability to skip a test based on the runtime being used

[jodh-intel]

Currently, some of the tests make use of Skip() (ginkgo). At some future point they will also be using skip (bats) too. These calls skip the tests unconditionally. However, we are likely to need ways to skip a test but only for particular runtime(s) [1]:

Something like:

if kata.Runtime("cc") {
    Skip("Issue: ...")
}

We should also support any:

if kata.Runtime("any") {
    Skip("Issue: ...")
}

... and maybe a regex like:

if kata.Runtime("cc|runv") {
    Skip("Issue: ...")
}

We'll need kata.Runtime(name string) to check to see which runtime the kata-runtime symlink actually points to. If the link name ends in -cc [2], it's a Clear Containers-based runtime, else runv.

We can then compare the fully resolved value of the Runtime path with the runtime type the test is requesting be skipped and return true/false as appropriate.

---

[1] - runtime names should be specified using the same syntax as used for the build. Namely cc or runv (or all). See kata-containers/runtime#16.
[2] - Or, run the runtime and check for a known string such as:

$ kata-runtime --help | grep -q clearcontainers

[grahamwhaley]

Just a thought, not sure if we can use it here - but, I have seen another project using the golang build constraints to mark which test files are runnable dependant on which variant is being built:
https://golang.org/pkg/go/build/#hdr-Build_Constraints

Just putting that out there as a potential slightly higher level option for if we get any tests that fall into that sort of build dependent category.

[egernst]

we only have kata-runtime now -- let's close this. No need to add this complexity.