init: Make init script configurable

Init script loads /etc/sysconfig/corosync (or /etc/defaults/corosync) by
default, but it didn't existed by default and also no options was
defined.

Patch adds COROSYNC_INIT_TIMEOUT (how many seconds to wait for ipc
initialization) with default value 1 minute (instead of previous 10
seconds, what may be too small value for some productions) and
COROSYNC_OPTIONS (by default empty) containing options directly
passed to corosync executable.

Specfile template is also modified to install example of init file
configuration.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>