Remove "/etc/group" from the list of recommended bindings.

Some packages can't be installed because they fail to add or remove an
entry in this *host* file.

Change-Id: I4cc9a41b55e0e9e483b01dc162dcd895c715ffe3
Don't fail if the Unix domain socket test-case doesn't have enough permission.

Some validation environment have restricted network access (Trvais-CI,
for example).

Change-Id: I2b80cbbf0ff7e881b278adcd781ea510480c7e40