core: Handle SIGPIPE

As we don't want the daemon to terminate when it gets a SIGPIPE because a client
closed the connection before or during a write, ignore the signal and just
terminate the client after write fails.
test: Improve fail logging

Signed-off-by: William Douglas <william.douglas@intel.com>
shared: Set return to true when call is complete

Signed-off-by: William Douglas <william.douglas@intel.com>
test: Add buxton_wire_get_value check

Signed-off-by: William Douglas <william.douglas@intel.com>
cli: Add callback for get_value

Need callback in order to output value from daemon.

Signed-off-by: William Douglas <william.douglas@intel.com>
cli: Add callback for unset_value

Need callback to output value from daemon.

Signed-off-by: William Douglas <william.douglas@intel.com>
demo: Fix timing callback

Get return value from daemon in order to verify call was successful.

Signed-off-by: William Douglas <william.douglas@intel.com>