inotifyx does not support Python 3.

It was reverted in commit 9c672830
but it is still required to bootstrap from old SlapOS setups.

Replace dropbear by openssh.
Use same rdiff-backup than provided by PBS.
Allow to directly use an IPV6 address with a custom port.

Add binding to a specific ip. 
Add error log. 

@rafael @gabriel 

/reviewed-on nexedi/slapos!256

Solve the problem that `slapos` script is missing from slaprunner ( described in !253 ) by adding `slapos.core` egg explicitly.

/reviewed-on nexedi/slapos!254

Thanks to nexedi/slapos!158 , in a slaprunner we can use slapos command:
```
$ slapos supply https://lab.nexedi.com/nexedi/slapos/raw/1.0.19/software/erp5/software.cfg slaprunner
```
works fine to supply a software to "current" webrunner, but building this software with `slapos node software` fails with:
```
$ slapos node software
2017-10-03 02:46:33 slapos[29536] CRITICAL slapgrid could not write pidfile /opt/slapos/slapgrid-sr.pid
2017-10-03 02:46:33 slapos[29536] ERROR [Errno 13] Permission denied: '/opt/slapos/slapgrid-sr.pid'
Traceback (most recent call last):
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/entry.py", line 300, in run_subcommand
    result = cmd.run(parsed_args)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/command.py", line 50, in run
    return self.take_action(parsed_args)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/cli/slapgrid.py", line 116, in take_action
    setRunning(logger=self.app.log, pidfile=pidfile)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/grid/utils.py", line 155, in setRunning
    write_pid(logger, pidfile)
  File "/opt/slapgrid/f496eadc03f1ac5a0ab1e4ae60bbe972/eggs/slapos.core-1.4.1-py2.7.egg/slapos/grid/utils.py", line 167, in write_pid
    with open(pidfile, 'w') as fout:
IOError: [Errno 13] Permission denied: '/opt/slapos/slapgrid-sr.pid'
```

because slaprunner's web interface also runs software, it's better both `slapos node software` command and the one from slaprunner web interface uses the same pid file so that they do not run in parallel.

This depends on nexedi/slapos.core!29

/reviewed-on nexedi/slapos!235

Since using apache-2.4[1] the Include directive will fail if no glob
matches, this switch to new, IncludeOptional[2], available since 2.4, in
order to not fail if no configurations are present.

 [1] 1f7bf3d1
 [2] http://httpd.apache.org/docs/2.4/mod/core.html#includeoptional

/reviewed-on !252

Recent versions of OpenSSL refuse to load Romain's key:

  unable to load certificate
  140268475908992:error:0D0E20DE:asn1 encoding routines:c2i_ibuf:illegal zero content:../crypto/asn1/a_int.c:154:
  140268475908992:error:0D08303A:asn1 encoding routines:asn1_template_noexp_d2i:nested asn1 error:../crypto/asn1/tasn_dec.c:609:Field=serialNumber, Type=X509_CINF
  140268475908992:error:0D08303A:asn1 encoding routines:asn1_template_noexp_d2i:nested asn1 error:../crypto/asn1/tasn_dec.c:609:Field=cert_info, Type=X509
  140268475908992:error:0906700D:PEM routines:PEM_ASN1_read_bio:ASN1 lib:../crypto/pem/pem_oth.c:33:

With older versions:

  Certificate:
      Data:
          Version: 1 (0x0)
          Serial Number: 0 (0x0)
      ...
Acked-by: Romain Courteaud <romain@nexedi.com>

On some machines, net:TestDialTimeout never passes and today, Go 1.4 is only
used for bootstrapping, so let's not be more clever than Go devs, who
explicitly state to use make.bash

See also https://github.com/golang/go/issues/18954

  id-store-interval is mandatory now.

See erp5@5169f193

Support for HTTPS added. 

@rafael @kirr @gabriel 

/reviewed-on !249