Add --mi option to the list command

The --mi option is used to ask lttng to print information in a format
easily understandable by another program. Currently, only session
printing is affected: it prints session names one per line.

The term mi stands for machine interface, and is stolen without any
remorse from GDB's lexicon.

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Add session name completion in bash completion

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: David Goulet <dgoulet@efficios.com>