[vault] additional status "absent"

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[unit] VAULT_GLOBAL_CONFIG_DIR can be used

VAULT_GLOBAL_CONFIG_DIR can overwrite global configuration directory
path

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #8 from deztructor/master

VAULT_GLOBAL_CONFIG_DIR and "absent" status