LocalVolumeType tmpfs added
Added checks to ensure tha volume created during setup contains expected testFileContent
Refactored tests out to avoid code duplication
Two different tests are performed with tmpfs:
-serial write and read in two different pods
-write and read in two different pods mounted at the same time
Fixed local storage test failures by integrating https://github.com/kubernetes/kubernetes/pull/50177
Switched NodeExec to SSH