Change GetExeDir to GetStateDir in Cedar and Mayaqua.

Resolve this AppArmor error by ensuring that certificate files files are
written into /var/lib/softether instead of the current working directory:

	Profile: /usr/sbin/softetherd
	Operation: mkdir
	Name: /usr/sbin/chain_certs
	Denied: c
	Logfile: /var/log/kern.log

	type=1400 audit: apparmor="DENIED" operation="mkdir" profile="/usr/sbin/softetherd" name="/usr/sbin/chain_certs/" pid=36448 comm="softetherd" requested_mask="c" denied_mask="c" fsuid=0 ouid=0