cli: print usage message when parsing of cmd fails
cli: print usage message when parsing of cmd fails

Signed-off-by: Pranith Kumar K <pranithk@gluster.com>
Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 1432 (print usage string in case of command parse errors)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=1432

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster