force the use of the $SALT_ETC_DIR instead of hardcoded /etc/salt

Impact on :

- config_salt()

- SmartOS install functions
Merge pull request #125 from virtua-network/fix_etc_dir

Force the use of the $SALT_ETC_DIR instead of hardcoded /etc/salt
Disable syndic test case.
Update change log
Merge remote-tracking branch 'upstream/develop' into develop