This PR enable tinyproxy to package as a snap. Also added conditional
for snap packaging by testing "--enable-snap". The reason here for
'--enable-snap' is that all services run as root thanks to confinement
in snap world and regarding system call(setuid, setgid) will trigger
apparmor "DENIED" error when running tinyproxy snap in confined mode.
Please refer to syslog here http://paste.ubuntu.com/24063282/.
