kvm tools: Generate list of common kvm tool commands

kvm tools: Generate list of common kvm tool commands

- The Documentation/ directory will have a text file for each commmand. The
  text file should contain the information about the command in manpage format.

- command-list.txt: is a list of common commands used with the kvm tool.

- util/generate-cmdlist.sh: is a shell script that uses command-list.txt and
  text files in Documentation/ directory to generate the common-cmds.h file in
  the include directory. The header file is furthur used to display a usage
  messgae. Almost the entire script is copied from the tools/perf.

Signed-off-by: Prasad Joshi <prasadjoshi124@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>