feat!: new kernel config structure

BREAKING CHANGE: kernel definition in the configuration files has switched

from

  [[targets]]
  distro = { id = "Ubuntu", release = "18.04" }
  release_mask = ".*"

to

  [[targets]]
  distro = { id = "Ubuntu", release = "18.04" }
  kernel = { regex = ".*" }

preload.go

@@ -102,8 +102,8 @@ func buildPreload(workPath, tmp string, ki config.KernelInfo,
 	ka.SourcePath = workPath
 
 	km := config.Target{
-		Distro:      ki.Distro,
-		ReleaseMask: ki.KernelRelease,
+		Distro: ki.Distro,
+		Kernel: config.Kernel{Regex: ki.KernelRelease},
 	}
 	ka.Targets = []config.Target{km}