prserv: use only PRSERV_HOST

- remove PRSERV_PORT variable
- use 'hostname:port' as PRSERV_HOST format
- use 'localhost:0' for enabling the local PRServer

[YOCTO #3744]

Signed-off-by: Constantin Musca <constantinx.musca@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
hob: hob do not use .hob dir for variables from local.conf and bblayers.conf

If .hob exists, hob takes the variable from there. Change to not override anymore
the variables which comes from bblayers.conf and local.conf

[YOCTO #2934]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>