kernel-shark: Add logic for selecting the trace-cmd executable used

If kshark-record has been started from its installation location it will
use the installed version of trace-cmd. Otherwise the trace-cmd executable
found by Cmake when building KernelShark (see FindTraceCmd.cmake) will be
used.

Link: http://lore.kernel.org/linux-trace-devel/20190502124009.32208-7-ykaradzhov@vmware.com

Suggested-by: Troy Engel <troyengel@gmail.com>
Signed-off-by: Yordan Karadzhov <ykaradzhov@vmware.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
3 files changed