Fix: lttng UI exit value and error message

Change lttcomm error code starting value from 1000 to 10. This way, bash
can return the exact error code since 255 is the maximum.

Fix multiple warning, error and message output.

Some return code could still be not "standardize" but for stable it's
ok. Fixes can come later on.

(close #105)

Signed-off-by: David Goulet <dgoulet@efficios.com>