We are sometimes seeing test failures when nodes can not register before the
beginning of the test, this promise make sure the grid is ready to use.

This was using system library.

     ldd ./parts/chromedriver-2.41/chromedriver
             linux-vdso.so.1 (0x00007ffc4b738000)
             libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f2aa9e46000)
             libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f2aa9e25000)
             librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f2aa9e1b000)
             libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f2aa9cfc000)
             libX11.so.6 => not found
             libnss3.so => not found
             libnssutil3.so => not found
             libnspr4.so => not found
             libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f2aa9b77000)
             libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f2aa9b5d000)
             libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2aa999c000)
             /lib64/ld-linux-x86-64.so.2 (0x00007f2aa9e53000)
             libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f2aa9928000)

mod_auth_web uses libcurl. Since 83f5929e (component/curl: version up 7.76.0,
including security fixes., 2021-04-07), our curl build depends on zstd.
Apply similar fix that 2f4d8cf8 (component/apache-php: fix missing libzstd, 2021-04-09),
ie. add zstd to rpath

update theia and some dependencies, including:
 - theia-open which should no longer segfault
 - buildout language server which should not report so many false positives

See merge request !958

These options are propagated by the switch_softwaretype recipe

forgot to update commit old software URL to point to the tag instead of the
work-in-progress branch used to test the commit.

see bd1b1928 (component/postfix: disable build on Linux >= 5, 2021-04-08)

supervisord unsets PATH and execvp falls back on the default value
  /bin:/usr/bin

See merge request !930

Sources of domains and IPs are:

 * default hardcoded in template/whitelist-domains-default
 * /etc/resolv.conf
 * provided in the request
 * provided in the special downloadble repository

Then they are parsed with dnsresolver and .slapos-whitelist-firewall file is
produced with list of IPs to be whitelisted.

This allows slapos.core whitelistfirewall manager to lock-down the partition
to only whitelisted list of IPs.

Provides dnsresolver tool.

See merge request !950

Even if boot-image-url-select is not designed to contain bad values, they can
happen, so add protection just like with boot-image-url-list.

Real images are not needed, so avoid big downloads from external resources and
just provide it via local http server.

Parameters coming from the user can result in having incorrect buildout
profile so dumps them for safety.

instance-kvm-export.cfg were copying parts defined in instance-kvm.cfg, but as
the latter one was evolving a lot, it was missing features.

For simplicity let instance-kvm.cfg expose the parts in a way, that
instance-kvm-export.cfg can blindly append the to list of own parts, as it has
to support resiliency exporter by itself.

Now that we updated postfix, we can use default openssl

According to http://www.postfix.org/announcements/postfix-3.1.2.html

> Fixed with Postfix 3.1.2:
> Changes to make Postfix build with OpenSSL 1.1.0.

Going Go1.15.10 -> Go1.15.11 brings in fixes to compiler, runtime and stdlib:

https://golang.org/doc/devel/release.html#go1.15.minor

Tested on helloworld SR (by adjusting it to use go1.15 instead of go1.16).