afb-ws-client: Improve direct URI

The direct connection URI was expecting a slash after the port
for "tcp:" URI.  This slash is not needed because it does not
carry any meaning. This change implements the ability to set
or not the path of URI.

Bug-AGL: SPEC-3094

Change-Id: I3d4c350f4e917759cbf82ccc0d261aa420f6f88a
Signed-off-by: Jose Bollo <jose.bollo@iot.bzh>