Initial work for kernel tracing support

Initial work for kernel tracing support

This commit adds trace kernel support to the complete set of tools. It
is working with the LTTng 2.0 and output traces readeable by babeltrace.
Quick changes log below:

Add multiple debug statement and bug fixes.
Add kernel trace directory creation.
Add kernel structure teardown.
Start kconsumerd on create session.
Start kconsumerd thread after exec.

Following up this commit, there will be a huge cleanup because a lot of codes
was added to make it work but it's not necessarily clean code structure.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>