allow setting post message from easyconfig file

[boegel]

In some cases, it would be interesting to allow setting the post message that is printed at the end of the installation process in the easyconfig file, e.g. for issuing warnings in case like bbcp which requires certain ports to be open for it to work properly.

The easyblock module already supports this via the self.postmsg class variable.

[Falkor]

+1 :) Have the case for LikWid where a setuid procedure is required for the daemon.

[boegel]

@Falkor What's the use case you have in mind?

[Falkor]

I just updated the easybuild recipes for Likwid that relies on the likwid-accessD daemon (built under $EBROOTLIKWID/sbin) to forwards the read and write requests to the MSR registers with higher priviledges as per [power] checks -- you will soon have the merge requests.

There are 3 ways to do that (setuid / setgid or libcap methods), only the first one actually works, but in all cases it would be worth to give the [sudo] commands to perform to the user.
So far, and unless I'm wrong, I can only do that by adding some messages as part of the postinstallcmds, typically as follows:

postinstallcmds = [
    'echo "IMPORTANT: you will have to manually apply the following changes:"',
    'echo "  sudo chown root:root \$EBROOTLIKWID/sbin/likwid-accessD && sudo chmod u+s \$EBROOTLIKWID/sbin/likwid-accessD"'
]

but that hides it in the build logs as they are not exposed to the user on the regular eb process.
In this case, having the possibility to provide post messages would be grateful.

[boegel]

@victorusu was looking for suggestions for contributions, maybe this is an easy one to tackle...

[PetrKralCZ]

I have implemented a solution with following usage:

postinstallmsgs = ["This is post install message 1", "This is post install message 2"]

== installing...
== ... (took 2 secs)
== taking care of extensions...
== ... (took < 1 sec)
== restore after iterating...
== ... (took < 1 sec)
== postprocessing...
== This is post install message 1
== This is post install message 2

• add support for postinstallmsgs #4145