Fix babeltrace-log(1) for Babeltrace 2

This fixes babeltrace-log(1) so that it works with the Babeltrace 2
tree.

What the program does now is to parse its arguments, create the
arguments to be passed to the babeltrace(1) CLI tool, and spawn a
babeltrace(1) process to build and run a processing graph.

babeltrace-log(1) executes babeltrace(1) as such:

    babeltrace run --component dmesg:src.text.dmesg --params read-from-stdin=yes
                   --params no-extract-timestamp=yes --component ctf:sink.ctf.fs
                   --key path --value /output/path --connect dmesg:ctf

`no-extract-timestamp=yes` becomes `no-extract-timestamp=no` with
babeltrace-log(1)'s -t/--with-timestamps option. The standard input is
forwarded to the child process.

Like babeltrace(1), the build system creates both babeltrace-log and
babeltrace-log.bin executables. The former spawns the in-tree
babeltrace(1) tool while the latter spawns the installed version.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>