Fix: missing memset 0 and NULL byte in string

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: return error if not in overwrite mode and file exists

For the save command, if the file is found and we are not in overwrite
mode, send back an new error indicating the client that the file already
exists.

Fixes #762

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: add missing string msg for save/load error code

Also, the LTTNG_ERR_LOAD_SESSION_NOT_FOUND has been removed and replaced
by LTTNG_ERR_LOAD_SESSION_NOENT.

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: add error/msg output to save command

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: rename config internal header to abi

Allow config ABI to be visible to the internal code.

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