lttng-tools: Improve ptest debugging and fix dependencies

lttng-tools: Improve ptest debugging and fix dependencies

Improve the ptest runner script:

* log output is available should any test fail to aid debugging
* document how to limit the runner to a single test
* stop hiding errors to stderr
* allow easier single test execution by avoiding path issues with PWD

Also depend upon binutils since one of the tests uses addr2line.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>