Initial import of the snapshot ABI/API in lttng-ctl

Nothing on the session daemon side as been added except the command
values added to the process client command subsystem.

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Add snapshot command to lttng UI

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Snapshot commands in sessiond

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] lttng snapshot command fails if session is not in no output mode

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Flight recorder feature

Signed-off-by: David Goulet <dgoulet@efficios.com>
[HEAD MERGE] Kernel snapshot support

**ADD CHANGELOG**

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] add kernel consumer destroy channel. NOT COMPLETED

Signed-off-by: David Goulet <dgoulet@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] free stream in the no monitor list on del channel

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] Some fixes. Veille technologique (RLNX inside)

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] destroy kernel channel fix

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] sessiond destroy metadata

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] close and free metadata stream on destroy channel kernel

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] add destroy metadata after metadata snapshot in sessiond

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] don't send metadata if session no output

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] fix crass malfait

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] fix crass malfait

Signed-off-by: David Goulet <dgoulet@efficios.com>
[MERGE] don't close metadata stream on del channel

Signed-off-by: David Goulet <dgoulet@efficios.com>
Squash 5 commits

fix channel/stream output mixup, return core and add basic test
close metadata
fix return code + validate trace multiple events
test files
enable all tests

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
fix refcount metadata no-monitor

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
fix return line

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>