inadyn: fix init script and default config file

This commit does a number of fixes to the inadyn package to make it
work properly "out of the box":

 * inadyn is installed in /usr/sbin, not /usr/bin, so we fix the path
   in the init script

 * Use "printf" for the Starting and Stopping messages, so that the OK
   / FAIL stay on the same line.

 * Pass the -q option to the start sequence, since it's passed in the
   stop sequence.

 * Fix the configuration file to use an existing dyndns_system and
   avoid a failure at startup.

 * Use a variable called ENABLED in /etc/default/inadyn to decide
   whether to start the service or not. By default, it is not started,
   as suggested by Gustavo, and an explicit ENABLED="yes" is needed.

 * Store the PID file in /var/run/inadyn.pid, like we do for all other
   daemons.

[Thomas: drop silly comment about uncommenting the alias line in the
configuration file, which is already uncommented. Noticed by Yann.]

Cc: Alex Suykov <alex.suykov@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>