This value is supposed to come from configuration file, which is already
implicitly provided inside used wrapper.

Back-porting a patch from upstream's github repository.

This reverts commit 18c4c3e2.

  Reduce a little the path+filename for the socket file, as NGINX/Linux has a limitation for long paths on this instruction.

  This small change allow the resilience test works w/o kernel patches or workarrounds.

Now we can run slaprunner's slapos just with `slapos`

For consistency and because mosh uses $SHELL and otherwise would use the
system shell ( /bin/sh )

~/bin/bash was used sometimes in place of bash, but we can use the
"real" bash directly, not need for a wrapper.

Introduce a section to define the shell $PATH and $SHELL we want to reference
from other sections.

slapos.cookbook:shell recipe creates a wrapper copying environment of
user running slapos node instance, but we are trying to avoid this.

For consistency, we want to use this shell when invoking `bash`

When connecting by ssh, bash starts with a $PATH containing standard
directories (/usr/bin:/bin). We don't want this to have priority either.

This simplifies 17931bed by not
overriding ~/.bashrc (that according to our ~/.bash_profile can be
modified by end users)

Because we have set a $PATH containing mosh-server it can be used with:

$ LC_ALL=C.UTF-8 mosh slapuser0@2001:67c:?:?:?:? --ssh='ssh -p 22222'

shellinabox shell wrapper, bash's .bashrc, gunicorn environment (which
minishell's inherit) and openssh command should all have the same $PATH
for consistency

Only use /usr/bin:/bin/ as a fallback.

Environment of user running `slapos node instance` should not influence the
instance.

Go1.5 and go1.6 are not used anywhere in slapos tree and neither these versions are supported by upstream release policy https://golang.org/doc/devel/release.html#policy anymore. So let's remove them.

/reviewed-on nexedi/slapos!239

This reverts commit 9b0b7a8b