[vault] do not copy result but move

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[api] list-snapshots should output snapshots list to the stdout

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[vault] non-zero return code if any unit is failed

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[backup] No tag if there are no succeeded units

It is allowed to tag backup if there is at least one succeeded
unit. In this way it is still possible to do backup of some units if
backup of other units can't be done. But it is useless to tag if all
units are failed

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[error] stupid bug is fixed

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #13 from nemomobile/cli-ret-error-failed-unit

Return non-zero if any unit op is failed, no tag if there are no succeeded units