This reproduces what happens on a Prod system, where
TokuDB turned out to use much more CPU than FileStorage.

  If the person wants to use slapos master, it makes no sense provide diferent options

There's little hope that it gets maintained because it contains a C extension whereas alternatives often use ctypes. In particular, it has no support for Python 3, and this is a blocker for us. At the beginning, [I though we were switching to pyinotify](0bb405fc): it is quite popular, and even used by fail2ban, but the code is ugly (big, crazy API, limited, and probably slow).

I didn't really know inotify and it's disappointing to see that created files (CREATE+WRITE+CLOSE_WRITE) can't be distinguished from hard links (CREATE). Acting upon new inodes is a common scenario and in the first case, you want to wait CLOSE_WRITE or you would read a partially written file. What I mean is that inotify is often unreliable, unless you detect changes done by your own software (e.g. you can make sure that files aren't hard-linked) but then some other IPC is probably simpler.

In any case, I open this MR because I haven't tested it. I only checked with pylint (hence the second commit).

/cc @alain.takoudjou @gabriel @luke (from Git history)

/reviewed-on !257

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 nexedi/slapos!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.