Bug fix for netdata alarm script

When sending test alerts, the /usr/local/libexec/netdata/plugins.d/alarm-notify.sh script raises the follwing error:

1. SENDING TEST WARNING ALARM TO ROLE: test
   2019-07-30 11:49:12: alarm-notify.sh: ERROR: Cannot find file ./../../../../etc/netdata/health_alarm_notify.conf. Using internal defaults.

The "../../../../" reaches the "/usr" folder, which doesn't have an "etc/netdata".

To fix this issue, the script need to be changed like this:

156c156
< [ -z "${NETDATA_CONFIG_DIR}" ] && NETDATA_CONFIG_DIR="$(dirname "${0}")/../../../../etc/netdata"
—
> [ -z "${NETDATA_CONFIG_DIR}" ] && NETDATA_CONFIG_DIR="$(dirname "${0}")/../../../../ local /etc/netdata"