MT#17781 Define NGCPCTL_BASE to fix PRO/Carrier installation

As soon as we merge 2e74d71 to ngcpcfg.git we cannot install PRO/Carrier:
> /usr/share/ngcp-ngcpcfg/functions/ha_features: line 54: cd: /etc /var: No such file or directory

Change-Id: I124adc4e42d3c87d0f4fbf19b076986d757cff39

etc/ngcp-config/ngcpcfg.cfg

@@ -3,7 +3,8 @@
 # Note:     do not modify unless you have a really good reason to do so
 
 # directory name where ngcpcfg is managed through git
-NGCPCTL_MAIN='/etc/ngcp-config'
+NGCPCTL_BASE='/etc'
+NGCPCTL_MAIN="${NGCPCTL_BASE}/ngcp-config"
 NGCPCTL_CONFIG="${NGCPCTL_MAIN}/config.yml"
 HOST_CONFIG="${NGCPCTL_MAIN}/config.$(hostname).yml"
 LOCAL_CONFIG="${NGCPCTL_MAIN}/config.local.yml"