An incorrect switch value should be pointed out clearly

[Praburaj]

An error to any switch value in kvm should clearly indicate the error first and print the usage.

Example:
kvm alias test2 0.1-alpha-build-0508 -x64 -scrc50

Notice svrc50 is incorrectly spelled as scrc50. The error message printed is
"Unknown command" followed by usage of kvm.

Pointing out the exact error will help in easier debugging.