cli: Implement version (--version,-v) option

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
cli: Fix segfault due to uninitialized client

We now ensure we have an initialized (NULL) BuxtonClient before we ever use
it, and only attempt to close the connection in instances where it is
appropriate, i.e. a new BuxtonClient is allocated.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>