Added support for hostless jobs to CLI

Added --hostless option to job create + few checks for parameters
incosistency (hostless implies no hosts, synch count labels etc)
and some unit tests.

Signed-off-by: Julius Gawlas <julius.gawlas@hp.com>
in GWT debug mode remove hop headers disallowed by Python 2.7

Added "hop headers" disallowed by Python 2.7 to set of
headers removed during the call, so one can use the gwt
forwarding for debugging with 2.7.

Signed-off-by: Julius Gawlas <julius.gawlas@hp.com>
README: Add link to mailing list and IRC info

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>