Revert "Add "/run" to the list of recommended bindings."

This reverts commit a133b4a88e2c91089826e59c9ab976bf0efdfdb6.

Binding "/run" by default wasn't a good idea because this breaks a lot
of programs that tries to write in "/run/var" (package managers
typically).
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